Advice needed on Altair Astro

[Ratcatcher]

I have always been fascinated by EEVA and am now in a position to have a go, to dip my toe in the waters to see if it is really for me.

As a 'toe dipper' I am thinking of this camera Altair GPCAM3 385C USB3 Colour Guide Imaging EAA Camera 

I would be mounting it on my pier mounted 125mm Celestron Astrofi (using Starsense) SCT

Any advice and user reports would really help me in making a camera choice.

Thanks in advance

Mike

[vlaiv]

That combination is going to be rather slow for EAA.

Sampling is 0.62"/px (very high resolution) and FOV is going to be tiny:

You won't be able to fit whole M13 on the chip as it is 0.33° x 0.19°.

If you want to use that camera, you will need some serious focal length reduction. Common thing to use is x0.5 FR in 1.25" format from GSO (and branded with other brands) - here it is from TS:

https://www.teleskop-express.de/shop/product_info.php/info/p676_TS-Optics-Optics-TSRED051-Focal-reducer-0-5x---1-25-inch-filter-thread.html

That item has FL of about 101-103mm, which means that it should be placed at about 51mm from sensor to give you x0.5 reduction factor. It will illuminate sensor the size of 385 chip, so you are good there. You can in fact place it further and get even more reduction - formula would be 1- distance / 102, so for reduction of x0.4, you would need to place it at:

0.4 = 1 - distance / 102 => distance / 102 = 1 - 0.4 => distance = 102 * 0.6 = ~61.2mm

Since this reducer is simple two element one - it will have some edge of the field aberrations. Just how much, that will depend on how much reduction you make it.

Alternative is to use dedicated reducer for that scope - and there is new one that will give you x0.4 reduction and is designed for SCT scopes, but it is very expensive, here it is:

https://www.teleskop-express.de/shop/product_info.php/info/p11425_Starizona-Night-Owl-2--0-4x-Focal-Reducer---Corrector-for-SC-Telescopes.html

0.4 reduction is going to give you 500mm focal length and sampling rate will be 1.55"/px - much better and I would say upper limit for EEVA/EEA applications (on most regular nights you don't benefit from going higher res even on long exposure imaging with very good mount and guiding) and FOV would be much better:

You can see that M13 is much better framed. Now FOV is just shy of one degree x half a degree, which is not far away from "perfect" EAA field of view of about 1-2 degrees.

Alternatively if you can get it - x0.33 reducer by Meade would be even better option.

Just a closing thought - 385 is rather good camera that will serve you as a planetary camera as well with that scope, so a good combo provided you can get it reduced to a factor of x0.3-0.4 for EAA.

[Ratcatcher]

Thanks for the detailed information vlaiv, I shall add a reducer to the list of things need. As soon as I am set up I will post results! Thanks again!

Kind regards

Mike

[Mike JW]

Hi Mike,

EAA is about getting an image reasonably quickly, (the idea of being "live") - there is much debate as to what might be reasonably quick.

To get an image as quick as possible: Increase the aperture, lower the focal length and use very sensitive camera (effectively pixel size).

Colour cameras are not as sensitive as mono cameras. Smaller pixels are less sensitive compared to bigger pixels.

The altair camera you are considering has small pixels and is colour and combined with the size scope you plan to use will limit what you will see.

I have limited understanding of software and my experiences of using the associated Altair software was nightmare to use. I tried the other suggested software - Sharpcap. I got on slightly better with Sharpcap. Both lack the ease of use compared to Starlight Live software. However the Starlight Software can only be used with Starlight Express cameras.

I use the Starlight Express Ultrastar (mono), other folk use the Lodestar (mono). Folk who have far more understanding/knowledge than myself use a variety of other cameras and software.

For a while I used a 5" refractor and a lodestar (mono) and got some very pleasing results.

Vlaiv is quite right to suggest a 1-2 degree fov for general viewing. I use considerably less fov as I am interested in distant galaxies but my narrow fov is useless for extended objects or large galaxies.

Mike