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Forum: Pentax Medium Format 5 Days Ago  
DxO finally published the 645z review....
Posted By whwang
Replies: 30
Views: 1,485
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: 34
Views: 2,274
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: 34
Views: 2,274
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: 2,924
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: 2,924
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: 2,928
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: 2,924
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: 2,924
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: 2,924
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: 875
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: 11,275
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: 11,275
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.
Forum: Pentax Medium Format 09-20-2016, 07:06 AM  
Fuji mirrorless medium format.
Posted By whwang
Replies: 152
Views: 11,275
The 23mm and 110mm lenses will be very attractive to astrophotographers. Now I can't recommend my peers to consider 645z for astrophotography. Sad.....
Forum: Pentax Medium Format 09-13-2016, 07:38 PM  
35mm F3.5 AL [IF] HD FA 645 Chromatic Aberrations
Posted By whwang
Replies: 13
Views: 929
Really? Let me make sure. We are talking about the latest 35mm for 645, right?
Forum: Pentax Medium Format 08-04-2016, 05:44 PM  
Post your medium format photos!
Posted By whwang
Replies: 11,126
Views: 1,803,936
No. It's a TAK. The on in this picture:
https://www.flickr.com/photos/weihaowang/20693423490/



Hi, ideally you will need to just get a P645 version of T mount, but unfortunately this doesn't exist. I can think of two alternatives. One is to first get a P67 mount, make an adapter to put it on your C11, and then get a P67-P645 adapter. This is the P67 mount I talked about:
http://www.mmjp.or.jp/takahashi-sb/data/tsring.htm#%83y%83%93%83^%83b%83N%83X67%83o%83%88%83l%83b%83g%8A%C2
Its front side is an M92P1 female thread. You can adapt it to C11 via a custom-made adapter.

The other possibility is to get the vixen P645 adapter:
http://www.vixen.co.jp/product/at/acc/373154.htm
Then you need to make another adapter to put this on your C11. Either way, you will need to make an adapter for C11. This is not that difficult if you know how to do it.

Is your C11 the HD version? The HD version should have a large image circle that can cover 645D's sensor. A standard version of C11 can illuminate a large area, but the outer part of the focal plan (even on 35mm full frame) would suffer from strong coma and field curvature. You may only get sharp stars in the very center part of your 645D image.

Cheers,
Wei-Hao
Forum: Pentax Medium Format 08-04-2016, 09:57 AM  
Post your medium format photos!
Posted By whwang
Replies: 11,126
Views: 1,803,936
Thanks. It's not a lens. It's a telescope. The focal length is 1100mm, and the focal ratio is F7.3.
Forum: Pentax Medium Format 08-03-2016, 11:29 PM  
Post your medium format photos!
Posted By whwang
Replies: 11,126
Views: 1,803,936
I think 645z is the best DSLR for astrophotography on earth. :) These are what I got last weekend.

γ Cygni and IC 1318 by Wei-Hao Wang, on Flickr

M8, M20, N6559 Region by Wei-Hao Wang, on Flickr
Forum: Pentax Medium Format 06-23-2016, 10:38 AM  
New Hassie Medium Format announced where next for Pentax 645Z and successor
Posted By whwang
Replies: 49
Views: 5,304
On dpreview I read that it will soon have a third lens and more lenses in the future and there will be a firmware update to enable electric shutter. I also read that the lenses are made by Nittoh. I can't confirm all these, so let's call them rumors rather than news.
Forum: Non-Pentax Cameras: Canon, Nikon, etc. 06-21-2016, 07:22 PM  
Hasselblad to announce a FF mirrorless camera
Posted By whwang
Replies: 119
Views: 7,004
To me, the biggest disadvantage of 645z is its array of lenses. If this new mirrorless can easily adopt more lenses, then it worths consideration.
Forum: Pentax Medium Format 06-19-2016, 06:44 PM  
Post your medium format photos!
Posted By whwang
Replies: 11,126
Views: 1,803,936
Thank you. I used an equatorial mount to track the motion of stars, so there are no star trails. The nearly 4 hr of exposure is actually composed of more than 80 3-minute exposures at ISO 800. The short-exposure images are stacked in post processing to reach an equivalence of 2-hr long exposures. Then the two 2-hr panels are stitched in Photoshop to form the panorama.
Forum: Pentax Medium Format 06-19-2016, 05:02 PM  
Post your medium format photos!
Posted By whwang
Replies: 11,126
Views: 1,803,936
I think so. After spending several months trying various 645/67 lenses on 645z, I decide to almost use it on my telescope exclusively. I will leave wide-field work like this to my D800 and Sigma Art lenses. With similar total exposure time, I can reach much better quality with D800+35/1.4 than 645z+35/3.5.

Pentax, wake up! This is the best camera for astrophotography, but it doesn't have good lenses. You used to produce one of the best astrographs, you should know this.
Forum: Pentax Medium Format 06-19-2016, 09:42 AM  
Post your medium format photos!
Posted By whwang
Replies: 11,126
Views: 1,803,936


Two-frame panorama made with FA35/3.5 @F5.6 and 645z. Total exposure is 4.35 hr.

The color aberration of this lens is very severe even at F5.6. This is not an ideal lens for astrophotography, and I doubt any of the current 645 lenses are.
Forum: Pentax Medium Format 06-15-2016, 06:41 AM  
Who is already using image transmitter 2?
Posted By whwang
Replies: 39
Views: 9,648
I played with it shortly using the local dealer's computer. I am quite disappointed. It's function is very limited, comparing to the free tethering software coming with my Canon 5D2 and the free software I used with my Nikon. The bulb exposure is not timed, as seanjmc mentioned above. The live view works, but it lacks reference lines/grids that the camera LCD has. The window cannot be enlarged and the live view zoom-in magnification is limited. I can't believe Pentax charges it $200 in the North America. (I did not ask the dealer in my country about its price, as there is no reason to believe it will be much cheaper.) $200 is not much comparing to anything I spent on the camera and lenses. What really makes me disappointed is the lack of functionalities, not the price.
Forum: Pentax Medium Format 05-12-2016, 08:56 PM  
Can I use outer bayonet Pentax 6x7 lenses on Nikon?
Posted By whwang
Replies: 7
Views: 743
Hi,
I am curious, what's the reason for using the outer bayonet mount? To have less vignetting? If this can make a difference, I would hope Pentax itself can produce a 67-645 adapter that uses the outer bayonet.
Forum: Pentax Medium Format 05-12-2016, 09:40 AM  
some star test results
Posted By whwang
Replies: 15
Views: 2,924
I added a few 67 lenses and create a separate Flickr account to just store the star test images. You can see them here:
https://www.flickr.com/photos/140916263@N04/sets/72157665841471914

Most of the test images are made from stacks of very short exposures (2 to 6 seconds). Later I realize that this cannot reveal color aberration, as shown by the P67 200mm/F4 case. So at some point all these tests need to be redone with longer exposures. This will be time consuming and also slightly more technically challenging. So I am not sure when I will have chances to do this, but I will try.

One issue I found long time ago and confirmed by these tests is that P67 lenses become out of collimation very easily. A good fraction of the tested lenses are out of collimation. The symptoms are not-round stars in the center or the shapes of stars in two opposite corners not mirroring each other. In the Flickr pages, you can easily see this on the color fringes of the 67 200/F4 and the shape of stars of the 67 75/2.8 AL. This is also true for my 67 ED 300/F4 on D800. So you should be really careful when you invest on a used 67 lens. The lenses may be good initially, but not so after a few years of usage.

Based on the data so far, and assuming that color aberration should be less an issue on shorter lenses, my ranking of the lenses tested so far for astrophotography is (from high to low):

1. 645 FA35/3.5 (needs to stop down to F5 or F5.6)
2. 645 DFA55/2.8 (needs to stop down to F5 or F5.6)
3. 67 90/2.8 (needs to stop down to F4.5)
4. 67 165/2.8 (needs to stop down to F4.5)
5. 67 75/2.8 AL (needs to stop down to F5.6)
6. 67 105/2.8 (needs to stop down to F5.6)
7. 67 200/4 (strong color fringing that doesn't go away at F5.6)

If I have to draw a line, I would say #6 and #7 are not capable of doing good astrophotography on 645z. #5 is the minimum I can accept, if the copy does not have collimation issues.

I hope at some point I can put my hand on the 645 DFA35, but this won't be any time soon, unfortunately.
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