Which files should I donwload from astronomy.net index mgr?

I need to determine which files to download from the Astronomy.net Index Manager but not sure how to choose. The first option is the “corresponding to about 20% of your narrowest FOV” and the second option is “corresponding to your largest FOV”. What file ranges should I select for an ES102mm APO Triplet, focal length 714mm, F7. Would I need to download additional files when using a focal reducer that makes the scope F5?
Thanks in advance for your help.


you’ll need to know your camera too. I’d then go along to one of the FOV calculators, such as astronomy.tools and plug all the details in.

Your smallest FOV will obviously be without your focal reducer, so get all the details in, and then find 20% of that FOV. Your largest will be with the Focal reducer, so there is your second parameter.

Dial them in, and go out for the day - it can be a long process to download them all, but thankfully you only need to do it once!

Thanks for the link Jim. I plugged my info in and the F7 FOV data is 1.42x1.07 - should I take 20% of 1.07? With the FR the F5 FOV data is 1.99x1.5 - should I stay on the high side here with 1.99?


I usually upload a sample image to Astrometry.net

Then look at the results it will tell you which index file it used to solve then I download that. It also shows you your exact image scale.

Note: Sometimes the index reported is located in their ‘wide field’ catalogue that is found on another link from their main website.

You’ve got it Mike.

I’d go for 0.2 and 2 (or the next one up just in case…)

Let us know how you get on!

Bingo. Loaded my files sets, opened an image from a previous session, right clicked and selected Blind Solve - 100% success. Confirmed RA and DEC. Thanks for the help!


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