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Forum: Pentax Medium Format 03-11-2020, 05:45 PM  
Telescope adapter for 645D
Posted By whwang
Replies: 22
Views: 2,003
Right. Not just that image, all side-by-side test images I took with the GFX50R are more noisy than 645 ones. They use the same sensor. So I suspect that the difference comes from the continuous live view, which keeps the sensor constantly working, and therefore generates lot of heat from the sensor and other internal circuits. Unfortunately I haven't had enough tests to verify that heat is indeed the cause of the extra noise in GFX.
Forum: Pentax Medium Format 03-10-2020, 09:08 AM  
Telescope adapter for 645D
Posted By whwang
Replies: 22
Views: 2,003
Did not see this thread before. I have an RAF adapter for P645. It fits the camera nicely, without problems, although I have never really needed to use it.

My telescope has a P67 adapter made by the telescope manufacture. Then I use Pentax's own 67-645 adapter to hook up my 645z. Earlier Stevein mentioned about Astrobin search results. The majority of 645z images you can find on Astrobin was taken by me. And this is my Astrobin gallery.

To be able to to use 645z on a telescope, the adapter is just one of the equations. There are two additional requirements, both of which are more difficult to meet than getting an adapter:

1. The telescope needs to be able to project a flat image circle that's large enough for a 44x33mm sensor. Not many telescopes can do this. It typically requires a large focuser, and a large, dedicated corrector lens (focal reducer, field flattener, or coma corrector, depending on the type of telescope). Most telescopes in the market are designed for APS-C or FF, and they don't have a focuser and a corrector lens large enough for P645.

2. The optimal focus point should be far away from the last lens element of the corrector lens, far enough to accommodate the humongous 71 mm flange-back distance of P645 plus whatever length for the adapter. Among all 645 cameras, P645 has the largest flange-back distance, and not just large, unreasonably large. Pretty much only telescopes that are designed for P67 (very few) can offer this kind of back-focal distance for P645. If we are talking about Fuji GFX here, things will look much better. There are some very nice telescopes that can accommodate GFX but cannot accommodate P645, because of the very stringent requirement on back-focal distance.

The OP wanted to hook up his 645D to C4.5. There is just no hope he can do it, and no point for him to do it. C4.5 does not have the kind of large back-focal distance for P645. Even if it somehow magically has, its focuser is way too weak to support 645D's weight. Even if the weight is not an issue and even if it can reach focus, C4.5 cannot illuminate a 44x33mm area with good image quality from center to corners. If it is an 8inch Newtonian instead of 4.5inch, then it starts to look feasible. It is possible to find a strong focuser to be put on an 8+inch Newtonian with a coma corrector that can accommodate P645 (TV BIG Paracorr).

645z is absolutely a powerful camera for astrophotography. Unfortunately only few telescopes can go along with 645z.
Forum: Pentax Medium Format 02-25-2020, 11:26 PM  
Come on Pentax where’s next 645 !?
Posted By whwang
Replies: 142
Views: 12,573
I think the current 645z is great in many ways, but can also benefit from many improvements like those mentioned in this thread. The real problem I see is that, Pentax just doesn't have the resource to do it. Just maintaining their FF and APSC lines plus a couple of new lenses every few years (not including those made by Tokina and Tamron with Pentax marks) already seems difficult enough for them. It will be a big surprise to me if they can do any major upgrade to the 645z line.
Forum: Pentax Medium Format 10-24-2019, 05:44 PM  
Come on Pentax where’s next 645 !?
Posted By whwang
Replies: 142
Views: 12,573
My guess is that we won't see a thing from Pentax even after there is GFX-50SII.
Forum: Pentax Medium Format 06-01-2019, 12:08 PM  
Come on Pentax where’s next 645 !?
Posted By whwang
Replies: 142
Views: 12,573
Actually I do that a lot. Really a lot. But, there is a limit: when your target moves. That happens when you have stars moving slowly on the sky while everything on the foreground is fixed. In such a case, it will be really hard to stitch multiple frames while giving each frame sufficient exposure time. Fortunately I don’t do this kind of photography very often, so I can live with the lack of good UltraWide, for now.
Forum: Pentax Medium Format 05-31-2019, 11:06 PM  
Come on Pentax where’s next 645 !?
Posted By whwang
Replies: 142
Views: 12,573
To me, the real problem of 645z is the size of the camera. That size was already the largest among all old 645 film bodies (judged by the flange-back distances), and is inappropriately big for a 44mmx33mm sensor. Because of the unnecessarily large flange-back distance, it's hard to make a good ultra-wide lens or an excellent wide lens, like those on the Fuji. This large camera body only makes (some) sense for a true 645 sensor. I really love my 645z, but I am very disappointed by the choices of wide/ultra-wide lenses on it, especially after comparing pictures taken with Pentax 25mm and Fuji 23mm side-by-side. I hope the next Pentax 645 camera (if there is one) can solve this.
Forum: Pentax Medium Format 03-31-2019, 07:21 AM  
NIKKOR LENS on PENTAX 645Z
Posted By whwang
Replies: 8
Views: 1,197
See this: http://www.galerie-photo.com/manuels/nikkor-lenses-for-large-format%20cameras.pdf

I believe these Nikkor lenses can be used on P645. The image circles are large, and many of them have flange focal distances larger than P645's requirements. You have to find the right adapter though.
Forum: Pentax Medium Format 09-05-2018, 08:25 PM  
The real 645!
Posted By whwang
Replies: 104
Views: 5,486
This is indeed a burden for Pentax. In some sense, the need of using legacy lenses also means a lack of new lenses. This has been complained on this forum for numerous times. Pentax isn't producing enough new lenses for 645D/645z. With this pace of making new lenses, there won't be enough lenses that can meet the requirement of 150MP 645 FF sensors. If Pentax does produce such a new 645 FF camera, those who spend lot of money buying it will find themselves in a situation where they have to adopt old/poor lenses. This really sucks.

A matter of fact is that among the legacy 645 systems, Pentax 645 has the largest flange back distance, 71 mm (as oppose to 63 mm for Mamiya 645 and 64 mm for Contax 645). This unnecessarily large flange back distance severely limits the performance of wide-angle lenses on 645D/645z. I have a fortune of using Pentax's DA645 25mm/F4 for a few days, and recently I got a raw file shoot with Fuji GFX-50S and its 23mm/F4. The Fuji's performance in terms of corner sharpness at wide open far exceeds the Pentax at even F6.7. There is simply no comparison in quality between the two. The extremely large flange back distance of Pentax 645 is the major reason for this difference, I believe, if not the only reason.

Given all the above, I truly hope Pentax can go mirrorless first, instead of going to 645 FF. The current Pentax 645 plate form is simply not good enough to support 150MP sensors. A 150 MP 645 FF sensor has roughly the same pixel density as a 100MP 44x33mm sensor. This (100MP) is twice more than what 645z currently has. If the lenses Pentax is producing are not good enough even for a 50MP sensor, how can we expect them to satisfy 100MP or 150MP sensors?

Don't get me wrong. I have been a loyal Pentax user since the 90s (Pentax 67). I really don't want to leave the Pentax system. However, if Pentax doesn't put itself together and compete, I may leave one day. Give me good lenses first, please, and then we can talk about 645 FF.
Forum: Pentax Medium Format 07-02-2018, 10:20 PM  
25mms - visually comparing DFA and DA examples
Posted By whwang
Replies: 9
Views: 1,298
What I always do is to put a piece of white paper (instead of the camera body) behind the lens and project a bright scene onto the paper. This way, you can immediately see which lens has a larger illumination area.
Forum: Pentax Medium Format 05-16-2018, 03:42 AM  
Who is already using image transmitter 2?
Posted By whwang
Replies: 43
Views: 11,363
The new timed Bulb mode is a welcome improvement. However, it has some bad bug, at least in the Mac version.

After I triggered a timed Bulb exposure, if I switch to a different desktop and do something else in a different program, IT2 times the exposure slower than what it should. This leads to exposures longer than what they are supposed to be.

So, be careful.
Forum: Pentax Medium Format 03-05-2018, 04:08 AM  
New 645z in 2018?
Posted By whwang
Replies: 83
Views: 16,414
I don't mind who makes it, either. It's just harder for me to imagine Tamron or anyone designing/making 645 lenses for Pentax. Pentax pretty much has to do it by itself.
Forum: Pentax Medium Format 03-04-2018, 11:06 PM  
New 645z in 2018?
Posted By whwang
Replies: 83
Views: 16,414


I saw this conversation on DPReview regarding Pentax's new 50/1.4 for 35 FF (K-1). It might be true. The new 50/1.4 from Pentax looks similar to Tokina's new 50/1.4. Earlier Pentax also had a new 15-30/2.8 for 35 FF, and it looks almost identical to Tamron's 15-30/2.8, including numbers of lenses and groups.

If this is true and Ricoh Pentax no longer has the capability to design high-end camera lenses, I feel very pessimistic about the future of its 645 line. Those who already have a few Pentax lenses that can cover the 50mmx40mm 645 FF might be willing to buy the new 645 FF from Pentax, but that's probably it. Those who are not in the Pentax camp will very likely think twice before they jump in, even if Pentax produces a 645 FF camera. Who will want to buy camera bodies from a company that is no longer capable of producing exciting new lenses to match the need of next-generation high-resolution sensors? I know I won't.

As a Pentax user for more than a decade (Pentax 67, Pentax's astronomical telescopes, and now 645z), I feel quite sad when I saw that.
Forum: Pentax Medium Format 12-12-2017, 06:04 AM  
New 645z in 2018?
Posted By whwang
Replies: 83
Views: 16,414
645z update? There is not a new 44x33mm sensor from Sony, except for the to-be-very-expansive 100MP one. Without a new affordable sensor, I don't see how 645z in the current form factor can be updated.

Pentax goes mirrorless? That will be very nice. However, given how slow they have been in the past few years in introducing new DSLR cameras or lenses, I can hardly believe they will produce a mirrorless medium format camera all a sudden.

I really want to see new things coming out from Pentax, but I don't have high hope.
Forum: Pentax Medium Format 11-15-2017, 07:53 PM  
DxO finally published the 645z review....
Posted By whwang
Replies: 34
Views: 3,350
Few weeks ago, DxO people commented on not publishing 645z's test results for years. They said that they did not publish a complete review because they don't have enough resource (or something like that). I was sort of buying it, and looking forward to their finally publishing 645z's result.

Now, I am very disappointed seeing the review. They already had the numbers two years ago. The most difficult part had been done already. And then it took them two years to come up with the simple text in the review? There is nothing new in the text they wrote, and it's not difficult to write at all.
Forum: Pentax Medium Format 02-23-2017, 09:45 PM  
645 and CP+ 2017
Posted By whwang
Replies: 31
Views: 2,935
I agree. I will be very happy if Pentax can surprise us, but I don't have a high hope on this.

In my experience, sample variation in lenses usually show up as asymmetry in stellar images, either stars that are not round in the frame center or the four corners show different shapes of stars. I have (or have seen) many Pentax lenses showing such, so my confidence level on the production accuracy of Pentax is quite low. However, on this 25mm/F4 (and my newer 645 lenses), I do not see such symptoms. So there is a good reason to believe it performs close to its design spec. The picture I showed originally have even worse stars in the corners. I did some Photoshop tricks to shrink the stars in the corners so the picture does not look as annoying as it originally was.
Forum: Pentax Medium Format 02-23-2017, 06:33 AM  
645 and CP+ 2017
Posted By whwang
Replies: 31
Views: 2,935
I am an astrophotography dude, and I won't hold my breath on such a lens. After seeing how the 25mm/F4 performs on stars, I am not going to believe Pentax can produce a 21mm lens that is useful for astrophotography at any aperture faster than F5. It's either that Pentax doesn't have the technical capability or the limitation of Pentax 645 form factor (long flange back distance), doesn't matter. I just don't believe a good wide-angle lens will be ever produced by Pentax for 645z for astrophotography.

see:
ALMA and the Magellanic Clouds | Stack of 8 20-second exposu? | Flickr
I have to stop it down to F5.6 to make myself semi-happy.
Forum: Pentax Medium Format 02-06-2017, 05:54 AM  
some star test results
Posted By whwang
Replies: 15
Views: 3,636
Thanks for the info. It makes me feel better if the new 35mm only has different coating. I purchased the old one only a short while before the new one was announced. If coating is the only difference, then I will like/dislike mine as much as if it is the new version.
Forum: Pentax Medium Format 02-02-2017, 02:47 AM  
some star test results
Posted By whwang
Replies: 15
Views: 3,636
Unfortunately I don't have access to this lens. I hope I can have a chance to test it.
Forum: Pentax Medium Format 12-08-2016, 09:36 AM  
Pentax 645 to Fuji / Hasselblad? Anyone considering the switch?
Posted By whwang
Replies: 38
Views: 3,946
I will keep my 645z and use it with my telescopes for astrophotography, until it is completely outdated, which will not happen in the next 3 to 5 years. That's for the camera body. On the other hand, some of you might have seen in another thread that I do not like Pentax lenses at all. So I might end up with getting the Fuji and see if its lenses match my need. (Probably not, but I have to try to tell.) Two weeks ago I had a chance to play with Hasselblad X1d for a short while. I like its incredible light weight and compactness, but I do not appreciate its user interface. Its lack of focal plane shutter is the game stopper for me, meaning that I can't hook it up with any telescopes or 3rd party lenses. So I won't consider X1d. Only the Fuji one is on my radar at this moment.
Forum: Pentax Medium Format 12-04-2016, 11:27 PM  
some star test results
Posted By whwang
Replies: 15
Views: 3,636
Hi Obin,

Yes, all the things (or the similar) you mentioned came across my mind at least once in the past.

I have a Apogee F16M, which has the same CCD (KAF16803) as the G4-16000. I am not impressed by this camera (or cooled CCD in general), as its read noise is about 4x as large as modern CMOS. This severely limits its capability when used with RGB or H-alpha filters. The exposure has to be unreasonably long (under my F7 optics) to make the influence of read noise go away. I realized this after I wasted quite a few nights on this camera, and then I never look back. CCD is old technology, and CMOS is superior in many ways. Once there is a mono version of large format CMOS camera (cooled or not, doesn't matter to me, since I almost always image under cold temperature), I will seriously consider to abandon DSLRs.

AG's D-K has my attention for a long while. At this moment, I am more into wide-field mosaicking, so their focal length is kind of too long to me. However, I may want to shoot smaller things in the near future. Then I will give it a very serious thought. Indeed, it is the top one on my list if I do want to switch to longer focal length.

On the VSD, if one takes a somewhat shallow image, say 0.5 hr of total exposure, and compare it with TAK's FSQ, the two are basically on par with each other. They are equally sharp. The FSQ perhaps has a slight edge in the field center, while the VSD has a slight edge in the FF corners. However, if the integration becomes very long, the stars in the VSD image will start to blow up, while the FSQ stars remain tiny. This means that there is a tiny level of uncorrected spherical (or chromatic?) aberration on the VSD. It's also more expansive than the FSQ, which makes no sense.

Cheers,
Wei-Hao
Forum: Pentax Medium Format 12-04-2016, 07:27 AM  
some star test results
Posted By whwang
Replies: 15
Views: 3,636
Hi,

Thanks. I used the VSD a couple of times. I am not impressed by its sharpness, although the image quality is quite uniform (uniformly mediocre) across the FF.

Like what you said, I now believe it is not a good idea to use any lenses on 645z. I primarily use it on my TAK TOA150. I have its 67 flattener and 645 reducer, and both can cover 645z very well.

The cheap 8" Newtonians do not have coma correctors suitable for 645z, I am afraid. I have TAK Epsilon 180ED, and even that doesn't cover the 645z sensor. The very large flange-back distance of Pentax 645 also makes things extremely difficult. Not many correctors/flatteners in the market are design to have this much back focus.

Very unfortunately, I have to conclude that 645z is not a very good camera for astrophotography, despite the very good sensor in it. The new Fuji mirrorless MP has much shorter flange back distance, which will allow it to be put on many more telescopes. It is also possible that its lenses perform better than 645z's lenses. I am looking forward to this new system.

Cheers,
Wei-Hao
Forum: Pentax Medium Format 11-21-2016, 08:22 AM  
some star test results
Posted By whwang
Replies: 15
Views: 3,636
A friend of mine got a like-new 25mm/F4 and let me use it for a short while. I took some star test images with it. You can view them here:
P645 DA25/4 @ F4.0 on 645z | Reasonable sharp at the frame c? | Flickr
Click the left arrow to see images taken under different apertures.

The results disappoint me. Strong coma exists even half way through the frame. Essentially only the very center of the frame is coma-free. Color fringes is also there in the corners. And all these do not improve much after stopping down to F5.6, which is the smallest practical aperture for astrophotography.

Last week I took my 645z and this lens to the Atacama desert to visit a few astronomical observatories. This is one of the pictures I took:
ALMA and the Magellanic Clouds | Stack of 8 20-second exposu? | Flickr
I stopped the 25mm down to F5.6. Here you can see that stars in the center appear to be fainter than stars in the outer parts of the frame. This is an artificial effect, caused by the coma of this lens. Actually, it is much worse. I had use several photoshop tricks to reduce this effect in the above Flickr image. The original one can be found here:
https://dl.dropboxusercontent.com/u/15886389/645z_25mm.jpg
You can see how bad it is in its original form. The apparent brightness of stars is not uniform, and this is very bad for astrophotography. For comparison, this is an image taken with Nikon D800 and Tamron 15-30/F2.8 at 20/F2.8:
https://dl.dropboxusercontent.com/u/15886389/D800_15-30mm.jpg
You can see that the apparent size of stars is much more uniform across the frame, and the stars are reasonably sharp. And this is achieved at F2.8, without any stopping down.

So far I had tried the 25mm, 35mm, and 55mm, and none of them impressed me. I don't have a high hope for the 70mm, given how these three perform. The 90mm might be still impressive, but its price is quite prohibitive. I will probably never have a chance to use the 90mm.

Looks like FF is the way to go for astrophotography. Then lenses for 645z just do not cut it.
Forum: Pentax Medium Format 09-26-2016, 10:21 PM  
Pentax K lens to Pentax 645 mount adapter
Posted By whwang
Replies: 9
Views: 1,757
I am surprised that the Rokinon 8mm does not fully fit the 360 deg circle into an FF. The Sigma 8mm does. See this picture of mine:
http://www.astrobin.com/159762/

The flange back distance of 35mm lenses are much shorter than that of 645 lenses. So there is no convenient way (or entirely no way) to fit the lens to 645 and expect it to work. To adopt a 35mm lens to MF, you need to use a camera back rather than the full camera body. This is what I got after I fit a Canon 15mm fisheye to Mamiya 69 film back:
http://www.astrobin.com/77503/
I suppose you can do the same to an MF digital back, but I believe you will go through lots of troubles that are probably not worthwhile. Just getting a Sigma is much easier.

Alternatively, you can take a picture with your Rokinon 8mm, rotate the camera/lens by 90 deg, and take another picture. You should be able to get a full circe after blending them together.

Cheers,
Wei-Hao
Forum: Pentax Medium Format 09-20-2016, 10:43 AM  
Fuji mirrorless medium format.
Posted By whwang
Replies: 152
Views: 14,002
Thank you for pointing me to the Japanese market. I do go to Japan every once a while and shop for photo equipments. Unfortunately I checked the websites of Bic Camera and Map Camera and cannot find this lens. Yodobashi still lists this lens, but also says it is discontinued. I think it is fair to say that even if it still exists in Japan, it is hard to get. I can't recommend this lens to my astrophoto friends not because I don't know the performance of this lens, but because it is hard to get.
Forum: Pentax Medium Format 09-20-2016, 08:02 AM  
Fuji mirrorless medium format.
Posted By whwang
Replies: 152
Views: 14,002
Right, of course. We will need to wait and see how they actually play out. A big problem here is that it's not easy to find thorough test reports on MF lenses. For FF and APSC, we can check the reports on DxO or lenstip, but there are very few (or none?) similar resources for MF.



That's OK. Most astrophotographers don't jump on a train right away. It took them 2 years to believe Nikon D800 can be excellent for astrophotography, and now there are many adapters of D810A. It will take even longer for them to move to the MF. A few of my friends are interested in 645z. One of them had actually pulled the trigger, and it will take the rests of them months (if not years) to actually make up their mind. So waiting for a year and see how things go with the Fuji mirrorless is not a big deal. Just don't buy 645z right now. The kind of astrophotography I can do with my 645z at this moment is limited by the lenses. I don't want my friends to face similar problems.

---------- Post added 09-20-16 at 08:08 AM ----------



Do you mean the discontinued 25mm? I don't have one, unfortunately. I will have a chance to borrow one from my friend for a trip to South America in November, so I will see how it works. However, given that it is discontinued, I can't recommend 645z to people based on this lens. On real 645, isn't the old fisheye 25mm or 24mm? Which means 25mm wide-angle is too wide, probably. 23mm or 24mm on the current cropped 645 format is probably about right.
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