FX vs DX

[poider (Peter)]

Probably a silly question, but with my 1.5x cop sensor Nikon D7200 and my 2x Barlow I fill my Screen with the moon using the 150mm - 750mm F/L newtonian, wouldI get the same result with a Full Frame camera?
Or would it be smaller.... does the telescope just act as a big lens and do the same as a lens, apart from the extra light capturing ability from the FF sensor is there any other benefit from going FF?

[Mickoid (Michael)]

Peter, your image size will be the same but the field of view will be larger on the FF sensor, ie. you will have more area around your moon than the crop sensor, so it will appear smaller.
I don't see a huge advantage in FF unless you want wide field shots of your target. Most targets we shoot are quite small, so the crop sensor actually helps remove unwanted areas around the object that distract from whatever you're trying to capture. Some argue the FF sensor has the advantage of producing less noise than crop sensors but if you're cropping your FF, then it probably ends up pretty much the same. It really depends on what you're shooting, I wouldn't be upgrading my crop sensor to FF if all I was using it for was astrophotography.

[JA]

Originally Posted by poider

Probably a silly question, but with my 1.5x cop sensor Nikon D7200 and my 2x Barlow I fill my Screen with the moon using the 150mm - 750mm F/L newtonian, wouldI get the same result with a Full Frame camera?
Or would it be smaller.... does the telescope just act as a big lens and do the same as a lens, apart from the extra light capturing ability from the FF sensor is there any other benefit from going FF?

Hi P,

Yes the moon would appear smaller if you compared an equal sized Full Frame Image with an equal sized APSc (DX) sized image. the moon is about 0.5 degrees in diameter as viewed from Earth.

Your 750mm focal length telescope will have a 2.75 x 1.83 degree field of view on Full frame and 1.83 x 1.22 degree field of view on your APSc sized D7200 sensor, and unsurprisingly will appear 1.5 times larger in the APSc sized D7200 image.

Regarding noise, take a look at the attached comparison of 4 cameras: 2 Full Frame and 2 APSc-ish of similar vintage (including your D7200) using a composite of the DP Review studio test scene RAW, at ISO3200 and in both standard and low lighting and judge ....

Yes I know: It's a test scene and not astro, that the cameras are a few years old (but hold up VERY well), that the ISO is high (to show differences... although it's not unlike stretching or increasing the exposure in post) and that I could have chosen other camera examples, but you have to stop somewhere

Best
JA

[poider (Peter)]

Thank you both