Info needed on using a correcting prism

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Moonstruck
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Joined: Tue Aug 17, 2021 4:34 pm

Info needed on using a correcting prism

#1

Post by Moonstruck »

I have been doing a fair amount of planetary photography lately using SharpCap, and would like to photograph the planets so they are right-side-up, and not backwards. My telescope, a Celestron CPC 800 HD w/edge optics, produces an upside-down and backwards image, which is driving me crazy. From what I understand, most telescopes produce an upside-down and backwards image. But it is important to me that north is facing up, especially when looking at the red spot on Jupiter (which is in the southern hemisphere on Jupiter), and when looking at planetary polar caps. So, I bought an erecting prism to try to solve that problem. However, while the prism correctly shifted the image to right-side-up, the image was still backwards. Is there a specific type of prism I need to get that would correct both the upside-down and backwards problem? Or, if not, can the image be shifted somehow in sharpcap during capture, or in a stacking program during post-processing?
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Re: Info needed on using a correcting prism

#2

Post by admin »

Hi,

you can certainly flip/rotate your final image after stacking using pretty much any photo editing software, so that's one way out.

Depending on the model of camera that you are using, you may have controls available in SharpCap to flip the image (ZWO cameras have this, as do Altair cameras in RGB and Mono mode).

In general, the normal advice would be to minimize the amount of glass between the camera and the target, so take diagonals, prisms, etc out rather than adding them - this is because every mirror or glass surface introduces some distortion and reduces the amount of light reaching the camera a little.

I'm not sure if I have this part right, but if your telescope gives an image that is inverted both vertically and horizontally, then that is equivalent to a rotation through 180 degrees, in which case turning the camera through 180 degrees in the eyepiece holder should put the image back the right way up and the right way round (I think...)

cheers,

Robin
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