[johnha]

Thanks for the update. I wouldn't put the adapter back on the camera. If the optics allow, using a short extension tube (or an adapter for the P67 on a Pentax adapter if available?) would be safer - at least you could get the tube off the camera.

[TDvN57]

I ordered a "M65x1 female thread to Pentax 645 camera mount adapter", found in the link above and a "T2 female to M65x1 male thread adapter" from RAFCamera via ebay. They arrived relatively quickly from Belarus to California. I also ordered a 2" T2 nosepiece to go from the T2 to M65x1 adapter to my Meade telescope, from a place called Agena AstroProducts.

When I first put the assembly of adapters on my 645Z the whole thing seemed to turn nicely in the bayonet mount of the camera, but never clicked into place like a lens would. It spun with a bit of friction, then spun free. It would turn about 45 degrees, back and forth, in the camera mount, without locking into place. When I pressed the lens release button to try to remove it, it wouldn't move past whatever was stopping it from turning counter clockwise. I removed the nosepiece and T2 to M65x1 adapter to see if I could see what was preventing the removal of the adapter, but couldn't see anything causing the problem. I applied a moderate amount of force to try to turn it but stopped for fear of damaging the camera.

I contacted RAFCamera and got a reply within an hour. This was the verbal exchange:
"me:
Upon first use of this adapter ring it has locked onto the camera and cannot be removed. Do you have any tips on how to remove it from my Pentax 645Z?

rafcamera:
Hi!
Tight a helicoid bit stronger and use it to turn adapter counterclockwise (don't forget to press a lens release button).
Thank you.
Raf.

me:
Thank you for the quick reply. It should require no more force to remove than a lens, yet it will not turn while pressing the lens release button.

rafcamera:
A lens has much more convenient grip, and lens mounts are made of steel usually (not more soft aluminium alloy like our adapter).
Moreover, we trying to make more strict tolerances, so tension is higher than with native lens usually.
I tested these adapters on my old Pentax 645. May be it is bit worn and allows bit more easy adapter turning.
But you should have no issues removing it anyway. Never had such reports so far. Just don't know what went wrong in your case, sorry.
Please try to apply bit more force.

me:
Again, thank you for the reply. I have been able to remove it, applying much more force than expected. Thank you. When it was on the camera, the adapter would turn approximately 45 degrees freely, as if it were loose. But when turning to remove it, and holding down the lens release button, it would stop and not move until extreme force was applied. I note some anodizing has been removed in the process.

rafcamera:
Our adapters have no stop pins. Looks like you overturned it during installation. Just be more careful next time, or you may damage camera mount. Thank you.

me:
That seems like some critical information not found in the instructions.

rafcamera:
People just turn adapter till a lock click usually, so no special instructions required. Thank you."

I need to use my 645Z next month, so I haven't attempted to put the adapter back on yet, and may never do so.

The point of my post: Use extreme caution putting any adapter like this on your camera.

I just double checked to see if the adapter I bought from them will properly lock into place on my 645z and allow me to remove it again. Worked flawlessly. Yes the tolerance is tighter than a lens, but it fits really sturdy and solidly and it triggers the customary "click" on the camera mount when it locks into place.

I have no idea what caused yours to be a problem, perhaps I was lucky. Although I've mounted it on the camera previously I was a bit spooked by your experience and first mounted it on a 645 to K1 adapter, when that worked fine, I re-tested it on the camera. Also worked fine as I said.

[iCrop]

I just double checked to see if the adapter I bought from them will properly lock into place on my 645z and allow me to remove it again. Worked flawlessly. Yes the tolerance is tighter than a lens, but it fits really sturdy and solidly and it triggers the customary "click" on the camera mount when it locks into place.

I have no idea what caused yours to be a problem, perhaps I was lucky. Although I've mounted it on the camera previously I was a bit spooked by your experience and first mounted it on a 645 to K1 adapter, when that worked fine, I re-tested it on the camera. Also worked fine as I said.

Good idea to try it on a 'Pentax Adapter K For 645 Lens', so I pulled mine out to test it. At first, I put it on, it turned and was tight, but clicked into place. I removed the RAFCamera adapter and tried it again. The second time it was tight as well, but spun until it became loose and now it's stuck. It didn't 'click' the second time. Pressing the lens release button allows the RAFCamera adapter to turn slightly, but it will not turn enough counterclockwise to remove it from the Pentax adapter. Glad I didn't try it again on the camera. It seems to me now that the problem may be related to whether the lens release button is pressed when turning, or not. I usually hold down the release button until a lens locks into place, but that may not work for the RAFCamera adapter. If I am able to remove it, I'll try to test this further.

[whwang]

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.

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Last edited by whwang; 03-10-2020 at 07:32 PM.

[rdenney]

And this is my Astrobin gallery.

Thank you for posting a link to your gallery. Astrophotography has come a long way since I explored it 35 or 40 years ago, and your images are truly spectacular.


Rick "for whom photography and telescopes are separately time-consuming and expensive and together a bottomless abyss of cost and commitment" Denney

[kaseki]

...The majority of 645z images you can find on Astrobin was taken by me. And this is my Astrobin gallery.

....

957 integration hours. Wow! That is commitment. Also, thanks for the useful end-to-end description of the issues.

[SteveinSLC]

Good to see an expert chiming in here. Thanks for posting Wei-Hao.

Of general interest on the medium format front, looks like he has been doing some comparisons between the Fuji GFX 50R and the 645Z.

http://group.asiaa.sinica.edu.tw/whwang/old/misc/M42_GFX_vs_645z.jpg

On my large monitor, the 645Z image is pretty clearly less noisy.

[whwang]

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.