[FrankC]

Hi all,

Does anyone know if it's possible, and if so, how to connect a 645D to a Celestron C4.5 reflector telescope?

Thanks,

Frank

[ElJamoquio]

Sorry, no help.

But here's a manual.

ftp://downloads.celestron.com/pub/manuals/telescopes/c_series/31026_c4.5/manual/31026_c4.5.pdf

They reference 35mm. Didn't see anything about 645.

---------- Post added 08-11-14 at 05:48 PM ----------

Hmm. Looks like the standard method was a T-mount, which I don't think would allow a 645 flange distance.

[interested_observer]

It's going to depend on the image circle projected by the telescope. The 645 is going to need a larger image circle to take advantage of the larger sensor, then the 135. Also, the mass of the camera is going to be much larger that the scope, mount and legs are going to have to support.

• https://www.pentaxforums.com/forums/6-pentax-dslr-discussion/113178-astrophot...ml#post2895867

[TDvN57]

It seems there are no solutions available to connect a 645 to a telescope, at least not the regularly available scopes.

I have found an adapter for the 645 mount which has a 65mmx1mm female thread mount. Thus a typical 'T2' mount for the 645, although the diameter is somewhat larger than the more popular M42 thread.

See the link here:
M65x1 female thread to Pentax 645 camera mount adapter


I contacted RAF camera and asked if they could make an adapter that fits into the 65mm mount that converts it to a M42. The answer was yes for abt USD30.

This will enable you to connect a regular scope to the 645, although a good chunk of the sensor will be in the 'shade'.

Despite the cropped image result, I ordered mine and I gladly accept the reduced image circle just so that I can make use of the 645z's qualities.

If anybody has any suggestions up improve or build on this, please share your thoughts.

..

[kaseki]

OK, my thoughts are based on fundamentals for whatever they are worth. Note that I haven't taken the time to investigate this particular telescope, so my thoughts are generalities.

First, we must distinguish 'telescope' from 'telescopic.' A telescope, whether Galilean or Catadioptric or whatever, converts ray angles such that incoming parallel rays exit parallel, and parallel ray bundles differing in objective (primary lens) entry angle emerge from the secondary lens group (eyepiece) at some multiple of that angle called the magnification. Magnification equals the ratio of the primary to secondary focal lengths. Astronomical telescopes for private viewing have exit apertures near the nighttime pupil size. It is the human eye's lens that focuses the ray bundles down onto the eye's focal plane: the retina (and in particular, the fovea).

So what is desired is to take a telescope that has both primary and secondary lenses for viewing, and optically mate the secondary to a camera lens that has a field of view equal to that which the secondary has (equals what the primary has times magnification), and which provides an aperture at least equal to the size of the image bundle leaving the telescope secondary. This camera lens may be telescopic in glass design.

All of this ignores how such a pair of assemblies -- camera with lens and telescope -- can be rigidly mounted. Hauling an optical bench with mounting fixtures into the field seems undesirable. Yet some type of mount is needed that keeps them aligned.

The approach used for professional astronomical observation dispenses with both telescope eyepiece and camera lens and focuses the telescope objective onto the camera focal plane (usually film plates or giant imaging arrays). This approach, when applied to devices such as Celestrons and their ilk, requires that the objective focus point be beyond any structure that would mount an eyepiece and far enough back to get to the 645 focal plane (film plane or imaging array plane) if the camera abuts the telescope structure. Whether the entire focal plane is filled depends on blockage and the effective field angle of the telescope given its optical design.

If a telescope is designed to be convenient for 35mm photography, it might lack the features needed for MF focal plane imaging. One can imagine potentially using an optical device that re-images one focus to another, such as a macro lens, or a reversed macro lens. Available f/no would have to equal or be lower in value than the telescope primary's f/no. Perhaps the 1.4X teleconverter could be used for focus extension and image plane magnification.

[SteveinSLC]

There must be some kind of T-Adapter available somewhere. There are a few pics on Astrobin:
Search - AstroBin

Taken with a 645D and a Takahashi 150 refractor.

[TDvN57]

OK, my thoughts are based on fundamentals for whatever they are worth. Note that I haven't taken the time to investigate this particular telescope, so my thoughts are generalities.

First, we must distinguish 'telescope' from 'telescopic.' A telescope, whether Galilean or Catadioptric or whatever, converts ray angles such that incoming parallel rays exit parallel, and parallel ray bundles differing in objective (primary lens) entry angle emerge from the secondary lens group (eyepiece) at some multiple of that angle called the magnification. Magnification equals the ratio of the primary to secondary focal lengths. Astronomical telescopes for private viewing have exit apertures near the nighttime pupil size. It is the human eye's lens that focuses the ray bundles down onto the eye's focal plane: the retina (and in particular, the fovea).

So what is desired is to take a telescope that has both primary and secondary lenses for viewing, and optically mate the secondary to a camera lens that has a field of view equal to that which the secondary has (equals what the primary has times magnification), and which provides an aperture at least equal to the size of the image bundle leaving the telescope secondary. This camera lens may be telescopic in glass design.

All of this ignores how such a pair of assemblies -- camera with lens and telescope -- can be rigidly mounted. Hauling an optical bench with mounting fixtures into the field seems undesirable. Yet some type of mount is needed that keeps them aligned.

The approach used for professional astronomical observation dispenses with both telescope eyepiece and camera lens and focuses the telescope objective onto the camera focal plane (usually film plates or giant imaging arrays). This approach, when applied to devices such as Celestrons and their ilk, requires that the objective focus point be beyond any structure that would mount an eyepiece and far enough back to get to the 645 focal plane (film plane or imaging array plane) if the camera abuts the telescope structure. Whether the entire focal plane is filled depends on blockage and the effective field angle of the telescope given its optical design.

If a telescope is designed to be convenient for 35mm photography, it might lack the features needed for MF focal plane imaging. One can imagine potentially using an optical device that re-images one focus to another, such as a macro lens, or a reversed macro lens. Available f/no would have to equal or be lower in value than the telescope primary's f/no. Perhaps the 1.4X teleconverter could be used for focus extension and image plane magnification.

I think it is safe to say that the M42-M65 adapter for the 645 will be agnostic to what the user connects to the adapter.

[rdenney]

You’re missing his point. Let me explain it a different way. If you project the telescope’s primary objective, which for the typical Celestron is the combination of the corrector lens on the front plus the primary and secondary mirrors, directly onto the sensor, then the sensor has to be close enough to allow you to focus at infinity. The 645 body is too deep for that, unless the telescope was designed for it. If it’s farther away than that, it will focus closer than infinity only, which isn’t useful for astrophotography. Some large amateur scopes, often home-built, were designed for Pentax 6x7 cameras, as I understand it. Those would work.

If you have to remove the focuser (which isn’t possible/useful in any case on most cats) to get the camera sensor at the primary’s focus plane, then the camera has to be mounted at exactly the correct distance to focus at infinity, which isn’t practical for the stuff you’ve been exploring.

Two options were mentioned. One was to use an optic that would extend the focus distance by magnification, such as a teleconverter. I’ve never played with that or really even thought it through.

The other alternative is eyepiece magnification, where you use an eyepiece, and the focus on the airy image projected by the eyepiece. The camera takes the place of the human eye, which focuses at infinity but has about a 7mm pupil. Doing this is...hard. Mounting must be rigid, the magnification steals a lot of light, and on and on. I’ve read about it but never done it. This makes high magnifications possible, but the greater the magnification, the more any tiny flaw in the system will be enlarged.

So, before investing in custom adapters, make sure the scope will project a sharp image as far away as where the sensor will be once the camera is mounted on the focuser, with no eyepiece installed. You can check this by using a hand-held ground glass, with the telescope pointed at some distant mountain during daytime (NOT the Sun!).

The typical 8” cat has a focal length of 2000mm, as I recall. You’ll end up with a camera that has 2000mm lens on it. More magnification requires more optics—a teleconverter or eyepiece projection.

Then, of course, there’s the issue of the mount, and its ability to stay rigid and track properly with that beast of a camera hanging off the focuser. I’m sure you’ve considered all that already.

Rick “whose 8” Meade Newtonian couldn’t possibly do this” Denney

---

Last edited by rdenney; 01-25-2020 at 09:47 AM.

[kaseki]

One thing I neglected to include commenting on is curvature of field. If the telescope image field is only flat enough for 35mm, or worse, only for a 7-mm eyepiece, the image on a ~50-mm width focal plane sensor may only be useful near the center anyway. In that case, a 35 mm to MF adapter may be a practical limit.

Also, it now occurs to me that given the objective's f/no, to get a ray bundle that is fairly big, one has to choke up on the bat, so to speak, and move the "eyepiece" optics closer to the objective. This greatly reduces the magnification. I think this is true even if a pile of glass moves this field diameter behind the telescope without actually physically closing the distance to the objective. The limitations imposed by the Lagrange Invariant are ever present.

[rdenney]

One idea for astro work I’ve considered is widefield photography. It’s much easier to piggyback a camera and its own lens on an equatorially mounted scope, and then use the scope for guiding. A 645z with a 400/5.6 would be optically pretty good—better than just about any affordable telescope—and could be mounted in lieu of a finder scope on a large amateur telescope. Or even ditch the scope and use the equatorial mount.

It’s not the strategy for planetary nubulae, but for larger chunks of sky can do interesting things.

Rick “never with the time or motivation to move this past arm-waving” Denney

[desertscape]

The telescope in question is a Newtonian. They are dominated by coma, so the image degrades pretty quickly from the optical axis, making them difficult to use photographically. The slow Newtonians (f/12) are a much better choice for photography.

[rdenney]

The telescope in question is a Newtonian. They are dominated by coma, so the image degrades pretty quickly from the optical axis, making them difficult to use photographically. The slow Newtonians (f/12) are a much better choice for photography.

Yes, but even more demanding of a solid mount because of the required longer exposures.

Astronomy, as Richard Berry once wrote, is a deep, dark jungle of obsession. Astrophotography is at the other end of that jungle, down a hole, and at the bottom of a cave. I think I colored up what Berry actually said

Rick “who hasn’t had the scope out in years” Denney

[nightfly]

An f/6 Newtonian has a 1" coma free image which is ideal for the 35mm frame. Faster coma free fields in faster Newtonian telescopes require a coma corrector. Of course this also requires a fully illuminated field, which would be at least a 2" focuser and an adequately large secondary mirror.

Large refractors, such as those make by AstroPhysics and TEC ($$$$) covered 6x7 film with exotic glass and correctors.

[iCrop]

I have found an adapter for the 645 mount which has a 65mmx1mm female thread mount. Thus a typical 'T2' mount for the 645, although the diameter is somewhat larger than the more popular M42 thread.

See the link here:
M65x1 female thread to Pentax 645 camera mount adapter

Despite the cropped image result, I ordered mine and I gladly accept the reduced image circle just so that I can make use of the 645z's qualities.

If anybody has any suggestions up improve or build on this, please share your thoughts.
..

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.

[barondla]

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.

Scary story. I've seen T mount adapters before with bad or missing stop pin. It isn't fun. I was considering one of these adapter set ups. Will pass for now. You might be able to add a stop pin to the adapter.

Thanks for the info,
barondla