mikedent Loc: Florida

Hello- I am using Canon crop-sensor with T-adapter to do photos of moon etc through my Celestron reflector. If I switch to a full frame body would the apparent view be smaller than the crop-sized view? ie would it negate the 1.6x crop factor "magnification"? Thanks!

Europa Loc: West Hills, CA

As I understand it, the factor still applies to your reflector.

mikedent Loc: Florida

OK, thanks, I was wanting to make the Moon image smaller so all would fit into the frame, was hoping full frame body would allow that- Mike

Europa Loc: West Hills, CA

Perhaps I needed to state that a different way. The crop sensor increases the focal length, ie makes the picture larger (zoomed in), by the 1.6 factor. The telescope will do the same thing that would happen with a lens. The full frame will reduce the size of the moon, well not really reduce it, It’ll capture more of it.

mikedent Loc: Florida

"It’ll capture more of it." That's what I'd like to do, so the entire Moon is in the frame instead of only a portion of it. Still looking for a used inexpensive Canon FF body for this.. thanks!

Europa Loc: West Hills, CA

You can try some different equipment to see what FOV you would get on this site:

https://astronomy.tools/calculators/field_of_view/

JimH123 Loc: Morgan Hill, CA

You might also try to find out if your scope can support a full frame camera without vignetting. Many scopes will support it. Some won't. What model Celestron scope do you have? Maybe someone who has that scope can comment.

mikedent Loc: Florida

Thanks- I have 130SLT reflector. Have not had any vignetting with the crop-frame body; yes, I don't know yet how FF would do.

JimH123 Loc: Morgan Hill, CA

I have been googling the 130slt and I do see that it has a 2" focused. But I also see that when using a camera, that it does not have sufficient in focus to allow infinity prime focus unless a Barlow lens is used.

I am guessing that you are using a T-adapter with a 1.25" adapter to fit into your Barlow which in turn fits into the 1.25" socket on the scope?

This being the case, a full frame camera is going to vignette a lot. A full frame camera captures an area that is approx 2.5x the area seen by a crop sensor camera, and when restricted to 1.25", you will see vignetting.

One solution I saw talked about was moving the mirror forward so that a true prime focus could be achieved. It wasn't mentioned just how easy or how difficult this might be. To be able to image without the Barlow would give you a FOV that is 2 or 3 times wider, depending upon the Barlow power you are using, and without the Barlow, your current crop sensor camera would likely be wide enough to see the entire moon.

Now let's suppose that moving the mirror forward is as easy as drilling new holes to mount the mirror farther forward. What would be needed next is a way to do a collimation. Celestron does sell a special eyepiece that shoots a low power laser beam back into the telescope that allows for adjustment to properly align the mirror.

You can Google collimate telescope and find instruction on how to do this.

SonnyE Loc: Communist California, USA

Another option that I like is something in a zoom lens.
My biggest is a 150-600 mm Tamron. I have always liked being able to "tweak" my shot with zooming.
I can fill the frame, or back away.

mikedent Loc: Florida

Yes the 130 is capable of a 2" focuser, but I am using the 1.25" one. I do have the Celestron Barlow specific for this scope prime focus ability. I can't see myself repositioning the mirror, I'm not that mechanically blessed! But if a FF does vignette here, would it still matter, if the main subject is centered in the frame, not at the outer borders? I've read around on various articles on this and they did mention vignetting possible but did not specify how bad it could be. Maybe it depends on the specific scope being used? AP can become a deep rabbit hole!

JimH123 Loc: Morgan Hill, CA

I ran an experiment today. We have a big storm moving in and it is getting darker by the minute, so I couldn't wait very long to do this. Took a guide scope and equipped it with a 1.25" eyepiece socket. And then I used a 42mm T2 adapter and inserted a 1.25" nose piece. Using this seed pod from the palm tree on the other side of my back fence, I first used the Sony A6300. Then I switched to the Full Frame Sony A7iii. You can see the vignetting effect. All these palm seeds are going to cause me grief in the spring when I have a gazillion palm shoots coming up all over the yard.

By the way, a Full Frame should actually use a 48mm T-adapter. I had one out and ready to use, but I couldn't find a 1.25" nosepiece that uses a 48mm T-adapter. Maybe I don't have one. I suspect that the 48mm T-adapter would not have changed things very much since the 1.25" nosepiece was already doing the vignetting.

I have gone back and added a rectangle in the Full Frame image to represent where the crop sensor image would be to help judge the effect.

Sony A6300; 1.5x crop sensor

(Download)

A7iii Full Frame sensor

(Download)


(Download)

mikedent Loc: Florida

Thanks, that's a lot of time and effort for this! I see the vignette effect. I also see the increased apparent field of view with FF which may help get the entire Moon in the frame, then could crop out the borders. Do you think the vignetting would be eliminated using a 2" focuser and correct T diameter? Might not be worth it money-wise with this scope?

JimH123 Loc: Morgan Hill, CA

It would improve it a lot. The 1.25" opening is not suitable for full frame.

mikedent Loc: Florida

OK, so I can get 2" focuser and correct T adapter from Celestron? May need to write them and ask specifically what I would need. Thanks!