Ags

I suggest you try this out with some eyepieces. Also refer back to the helpful diagrams posted earlier by @vlaiv

Except stars - their brightness remain constant regardless of exit pupil, except when exit pupil exceeds eye pupil, in which case stars get dimmer.

As an experiment I tried splitting Izar tonight with my ST80, barlowed with a cheap barlow. At 120 magnification there are certainly a lot of abberations to look at! The false color was of course expected, but it appears the ST80 needs collimation really badly (or the barlow does) - stars were showing as actual lines. Nevertheless, there was a definite split. The double double was a bit more dicey but one of the pairs split - the other would have split but was oriented badly versus the collimation issues. Well, if a battered old ST80 can do it, a nice little ED will definitely do it.

The beams come from different parts of the eye lens, and converge to the exit pupil. But the light for each point on the image (e.g. star) remain parallel and the light for each point does not converge in itself - but the light from the whole image converges. They are "beams of parallel light" NOT "parallel beams of light". Think of five people shining torches in your face. Each torch's light is (roughly) parallel, but the five beams of light converge on your face. That is what the light from five stars would do, each emerging from a different part of the eye lens and converging on your pupil.

This is incorrect. The exit pupil is the beam of light for every part of the image formed by the eyepiece. If you have an exit pupil of 5 mm, that means that each star in the field is represented by a beam of parallel light 5 mm in diameter emerging from the eye lens of the eyepiece. All of those bundles of light converge to a point above the eye lens (forming a disc 5 mm wide), and the height of that point of convergence is the eyepiece's eye relief. So when your pupil meets the disk at the eye relief height, it occludes all parts of the image equally (assuming the eye pupil is smaller than the exit pupil).

I am looking for a small refractor that can get to 3 degrees field of view with 1.25" eyepieces and still split my favorite doubles - Double Double, 61 Cygni, Izar and similar. Would a 72ED do the job? Or should i rather look to 80mm F6 refractors? There is this - but I think it will show too much false color at high magnifications (I want to see the double stars in their correct colors): https://www.teleskop-express.de/shop/product_info.php/info/p11436_Long-Perng-90-mm-f-5-5-Apo-with-Doublet-Objective-and-2--RAP-Focuser.html It is also at double my budget....

My C6 is similar to the mak in terms of focal length, and I use it quite happily giro-style on a Berlebach Castor.

As an AZ-GTi owner I would say no. I use a C6 on mine, but a 6 inch mak is much heavier. It's not goto, but you could dual mount the mak with a wide field frac - the frac can act as a superfinder for the mak.

Welcome to the forum!

@JeremyS and @michael.h.f.wilkinson Can I ask why 2-inch EPs are preferrable for you to 1.25" EPs with reducer? As I don't own any 2" accessories and don't plan to, the reducer seems logical - and will be much lighter (got to be kind to my AZ-GTi). And apparently the view with reducer will be more corrected...

@JG777 especially regarding sky background brightness, were you comparing at the same exit pupil?

I use a C6 on AZ-GTi when I want tracking or Goto features. The C6 is about at the limit of what I would put on an AZ-GTi but the result is good enough for me. the setup does very well for visual and takes some pretty good lunar pictures, well I think so anyway! I am even experimenting with photographing dim DSOs like star clusters, galaxies and smaller nebulae with the setup using millisecond exposures (Lucky imaging). The C6 plus AZ-GTi setup is for me the largest aperture I can get on my budget and still keep grab and go proportions. I can certainly say the fun stops when the scope gets too big. For purely visual astronomy I prefer the C6 dual mounted with a small refractor on a manual alt-az mount (Berlebach Castor). Last night I was using this to scan the moon at 230x magnification. On other nights the small (wide-field) refractor helps me hunt down the few DSOs I can see from a city. One thing to note is that a C6 is not a general purpose scope - it does extremely well on lunar and I expect planetary targets, and shows star clusters and galaxies well, but I do find it a bit underwhelming with regard to double stars. I have had a couple of smaller Maksutovs that have outperformed the C6 in the regard, both in terms of splitting capability and in terms of star shapes. So I am thinking of upgrading my refractor to remedy this. And the other shortcoming is an SCT is always limited in field of view - many interesting targets are quite large and the SCT is too "zoomed in" for them - the Pleiades and the Andromeda galaxy are two examples. I have attached a couple of pictures taken with my C6 and AZ-GTi - note these are from a severely light-polluted site. The kind of planetary photography you can do with the C9.25 Evo does not require a dark site.

Thinking of getting a Celestron 6.3 reducer for photography, but wondering if it might improve visual performance too?

Thanks all. I tweaked the design this afternoon, adding big washers behind the handles on both sides of the wood to spread the load. I have six slots to fill (a Super 25 and Super 10 are squatting in two of them). But this is cutting into my 72ED fund!

I completed my box. Added side handles, triple reinforced the base, double coat of varnish and I went 12 rounds with a enormous drill bit.

There was some chatter about the ES 52° series when it first came out, but not much follow up. Are these any good - comparable to a Televue plossl, or more like a generic plossl with more eye relief at shorter focal lengths? I hear that above 20 mm these are literally plossls??? I am thinking about getting the 3mm (for solar in a small refractor) and 30 mm (as a finder/alignment EP).

@vlaiv my C6 is indeed mounted on an AZ-GTi which copes reasonably well with the load. As it only weighs 3.3 kgs (the often quoted 3.7 kgs includes dovetail and eyepiece - a funny way to weigh an OTA) it is well within the load tolerance. There are cheaper 6 inch scopes and I have tried some of them, but they don't come lighter or smaller.

I got the base unit assembly complete today with only one ouchy finger.Tomorrow we varnish!

I'd like to see a picture of it with the Claves in place 🙂

The box does have an "eggshell" feeling of fragility to it. The base board I am adding with 1.25" holes will also be used to reinforce the bottom and sides as it will be fastened to the sides (and not just rest on the bottom). I will look at some metal brackets for nearer the top.

I got my wooden box today from Hobby Craft. It is very light. I am glad all the hinges and latches are attached with screws so they can be removed for painting. It is a bit rough and ready - I will need to lightly sand it to get the faces smooth and take the edges off the corners. I tried it with my eyepieces and there is a lot of empty space even after I add my Herschel wedge and barlow. The box was cheap, but filling those empty eyepiece slots is going to be pricey...

It's a bit of a lump (for a 1.25" eyepiece) but the Explore Scientific 24 mm 68° is superb.

I like the stain you chose, very retro. I have to ask: what is a Halloween Plossl?

I am working on 12 eyepieces, given a 7 cm square per eyepiece. EDIT: Looks like my maths was "a little" wrong - 15 eps is very reasonable.

I plan on using this: https://www.gamma.nl/assortiment/piranha-speedboor-34-mm-x52195-qz/p/B435884 I have trepidations - drilling such a wide bore can be tricky with the drill bit potentially catching. I plan on drilling 12 holes in a 28 mm thick solid wood base board, I will just take it slow and be careful. For carrying I plan on adding a pair of handles on the sides - I don't want the lid to take the whole load with a carry handle up top.