Connecting my DSLR to my SCT..?

[Astrowal]

Hi all, not sure if this is the correct place to post this, but here it goes; i tried connecting my DSLR (Canon 7D) to the telescope (Celestron 9.25 SCT) using a basic 1.25" camera adapter during the daytime to test it out as it was my first time doing so. Snapped a few photos at different iso and shutter speeds but each photo turned out pretty bad, colors were washed out, images were much darker than i expected, not to mention out of focus. Could the reason be that the 1.25" is not letting in enough light hence the washed out effects? 

[Louis D]

3 hours ago, Astrowal said:

Hi all, not sure if this is the correct place to post this, but here it goes; i tried connecting my DSLR (Canon 7D) to the telescope (Celestron 9.25 SCT) using a basic 1.25" camera adapter during the daytime to test it out as it was my first time doing so. Snapped a few photos at different iso and shutter speeds but each photo turned out pretty bad, colors were washed out, images were much darker than i expected, not to mention out of focus. Could the reason be that the 1.25" is not letting in enough light hence the washed out effects? 

Possibly you're seeing vignetting, though the sensor is only 27mm in diameter, the same as the clear aperture for a 1.25" adapter.  Take an image of the blank sky to see if there is light falloff toward the corners.

Colors will be washed out because your SCT has a large central obstruction.  That reduces contrast causing the washed out effect you're seeing.  This is apparently not an issue at night, though.  I tried using mirror telephoto lenses for daytime photography and quickly switched to refractor style ones because the contrast on the latter ones are so much better.  That, and out of focus highlights are donuts instead of round blurs.  Again, not an issue at night because everything is in focus at infinity.

As far as images being dark, try switching to manual mode and experimenting with different shutter speeds and ISOs to see if you can get lighter exposures.

As for focus, try live view on you camera LCD screen and increase the magnification to 5x or 10x to try to get better daytime focus.  Look for high contrast transitions to focus on.  At night, you can use a Bahtinov mask while focusing on a star to get good focus.

[Astrowal]

Hi Louis, thanks for the detailed explanation and the tips. Ordered a Bahtinov mask, should be arriving next week. I did try to focus on larger objects such as the moon and still wasn't as sharp as I would have liked it to be. Been reading on different forums about SCTs focusing abilities and the general concensus seems to be that upgrading to a microfocuser is the way to go. Will go for another try tonight hopefully get better results. 

Clear skies! 

[Padraic M]

@Astrowal I know what you mean - I've seen that with my Celestron 8" SCT and a Canon 400D.  The picture at night is generally fine, but I use flat frames to sort out the vignetting (as well as darks etc.)

There's an adapter that lets you connect a DSLR directly to the rear cell of Celestron SCTs by removing the visual back:. Might be worth a try.

https://www.celestron.com/products/t-adapter-for-schmidt-cassegrain-telescopes

[Astrowal]

@Padraic M I have a Baader 2 inch Clicklock attached to my telescopes rear. Ordered another DSLR adaptor with a 2 inch nosepiece so I can easily switch between diagonal and camera without having to unscrew the 1.25 inch adaptor everytime I complete the alignment procedure. 

Had to re-align about 4 times last night because I kept nudging the otp while switching between the two. 

Any experience in doing alignment with a DSLR attached? 

 

[Padraic M]

I don't even like touching the focuser! For alignment, I try to get in the region with the finderscope and then fine-tune through the DSLR. My camera is old (400D) and doesn't have live view so I have to do test shots on the laptop. It means not having to swap out the diagonal for the camera. It's not ideal, but the FOV with the APS-C sensor and the focal length of the SCT lets it just about work. btw, I normally use the 0.67x focal reducer. The SLR body is really too heavy to be stable on the back. Maybe adjusting the overall scope balance to account for the SLR might help.

I think, like you, I'll need to get  a shorter f/l refractor for photography. I got the SCT mostly for visual but couldn't resist taking some photos. I also need to upgrade my SLR - looking for a s/h 70D. This hobby is never-ending!