I am new to the hobby and looking to build out a 2 or 3 eyepiece collection for my Maksutov scope. (More equipment details and intended use details are at the bottom of the post).
I have noticed that eyepieces come in a wide range of AFOV angles from 40' in entry-level zooms to 110' super wide. And based on my reading, it seems like wide AFOV eyepieces show more context at a given magnification and provide an immersive space-walk like experience.
It seems too good to be true, so I wanted to ask:
- Are there any downsides to wide AFOV eyepieces (besides cost / weight)?
- Does stretching the view over a wider AFOV make the view dimmer compared to a narrow AFOV piece?
- How does a focal reducer / barlow affect AFOV and brightness / contrast?
- Wide AFOV eyepieces are expensive. Should I get one high-end eyepiece and use it with a barlow + focal reducer to have 3 usable magnifications? Or are there better strategies for covering a range of magnifications?
I am using an Orion Maksutov scope with 127mm aperture, 1540mm focal length (f/12.1). 1.25" Focuser. No electronics.
- I use my scope to see the moon, Jupiter, and Saturn from home since they are not affected much by light pollution and are visible on most nights.
- I hope to take my scope along on camping trips and start exploring deep space objects from national parks and dark sites.
3. Field size on the sky (true field) is related to magnification, so a doubling (Barlow) halves the width of the true field (not affecting the apparent field), while a focal reducer
enlarges the true field (not affecting the apparent field) by an amount related to the amount of focal reduction.
4. Your scope doesn't illuminate extremely large fields. Hence, I do not recommend the use of a focal reducer. The outer part of the field will be dark and you will not achieve the wider field you want.
Stick with 1.25" eyepieces, maximum field in the scope = 1.00° (sounds like it was planned. eh?)
You should have an eyepiece that yields a widest field. That could be:
40mm Plössl, 40°
32mm Plössl, 50°
24mm Wide field, 68°
Above that, you can use Barlows or more eyepieces.
All of those eyepieces have different apparent fields, but all yield the exact same true field in your scope.
The visual back on the scope has a 10mm threaded section for a certain type of camera adapter. By machining it off, you can move the diagonal closer to the scope, which shorten the
focal length of the scope to around 1510mm +/-, gaining you a tiny bit of field. Use of a prism diagonal shortens the focal length a bit more (though I haven't measured it).
Also, using a star diagonal with a full 28mm clear aperture all the way through, will help illuminate the outer edges of the maximum field.
Note that the scope's real aperture is ~120-121mm per the S&T test. I've verified this with a laser. So the f/ratio is a bit longer than the mfr. claims.
Here is a list of objects all of which have been observed in that very scope:
Edited by Starman1, 25 September 2021 - 01:31 PM.