Extra Flat 27mm or Starguider ED 25mm?

[Thalestris24]

1 hour ago, vlaiv said:

Maybe look into eyepieces for terrestrial spotting scopes then?

Or maybe not  - just looked at prices of those - way too pricey to be useful.

Yeah, Celestron do 1.25" EPs for their spotting scopes. But no worries, I'll wait and see what that Svbony aspheric is like and take it from there. Unfortunately, it's coming from the EU and there are delays... Estimated delivery is this Thursday but I'm pretty sure it won't get here until next week.

Cheers

Louise  

[Louis D]

First, does your scope use 23mm or 30mm barrelled eyepieces?  This is what ultimately limits the true field of view of any eyepiece in a microscope.  You can't see what's beyond the barrel.

Second, microscopes operate at high f-ratios (f/13+ as I understand it).  As such, they're not very demanding on eyepieces at the edges.

Third, I love my 23mm Aspherics in my binoviewer when barlowed to f/12 in my Dob or natively at f/12 in my 127 Mak.  It's super easy to get my nose between them and sink them deep into my eye sockets thanks to their diminutive size.  Being super light also makes scope balancing easy; although this isn't an issue for microscopy.

I also remembered I have unprocessed/unreleased 127 f/12 Mak images for several of the eyepieces I've mentioned here.  I whipped together a new composite image below for four of them. (Edit: I just added the Edscorp 25mm Abbe Ortho for reference).

As you can see, all perform really well at f/12 which is comparable to a microscope as compared to with the f/6 flattened ED refractor in the earlier image.

 

Edited February 22, 2021 by Louis D
Added Abbe ortho eyepiece for reference

[Louis D]

10 hours ago, Thalestris24 said:

On the face of it, it does look quite impressive for not very much! Can I ask exactly how you took the above image? 

Thanks

Louise

1. I taped some rulers and yardsticks together on their back sides with packing tape and then wedged them under the edge of one of my kitchen cabinets, but hanging off to the side.  I always align the 17 inch yardstick mark with the edge of the door for consistency.  I turn on every light in the kitchen/dinette area and open all the blinds to maximize the available light.
2. I put my AstroTech 72ED telescope on its leveled alt-az mount at the other end of our rather open plan house, about 35 feet away and close to level with the yardstick and close to perpendicular with it.
3. I put a 2" GSO dielectric diagonal in the focuser with a TSFLAT2 field flattener spaced 15mm in front of the diagonal body on the scope side.  This pretty effectively flattens the otherwise severely curved focal plane of the scope.  Luckily, I don't need to add any extension tubes to reach focus, unlike when I try this with a 127mm Synta Mak.
4. I put each eyepiece in the diagonal and focus the image with my eyeglasses on so the afocal image is focused close to infinity for the camera.  This allows the field stop to be at its sharpest if it was correctly positioned during assembly and allows the camera to focus at infinity.
5. I then center the yardstick in the field of view and lock the altitude clutch.  Next, I nudge the mount left/right to put the edge of the ruler at the edge of the visible field stop, or at least the edge of the field for those without field stops.  This can be a judgement call for eyepieces that use the barrel for the field edge as the edge will fuzz out.  Also, you can move your eye off center and see more of the field with them by peeking "around the corner" of them, so to speak.  That's why some don't show the edge when the camera is centered.  I'll sometimes take an image with the camera way off to the edge looking at the other edge at an angle to get a clearer image of this effect, just like your eye would be doing in this situation.
6. I use the high resolution, normal wide angle rear facing cell phone camera for most of my images.  In my case, a Galaxy S7.  I cup my thumb and forefinger around the top of the eyepiece to make a landing pad for the phone.  I start well away from the eyepiece and move the camera in toward the afocal image using the screen to guide my movements.  It's important to keep the camera level and centered.  That's where your thumb and forefinger come into play.  With practice, you can get it down to a fraction of a millimeter.  You can roll your fingers get fine height adjustment.  I've tried using adjustable height eye cups on eyepieces that have them to do this, but I couldn't get them to work very well.
7. Now, you have to move the camera phone in and out until the edge of field or field stop just pops into view.  You're at the correct exit pupil distance for that camera at that point.  Any further out, and you miss some of the field.  Any closer, and you start to get blackouts.  If there is spherical aberration of the exit pupil (SAEP or kidney-beaning), you're going to be fighting a dark shadow all around the field.  If you are perfectly centered, you will get a dark circle with a bright center and a bright edge ring.  This cannot be helped as it a defect of the eyepiece and not the camera or scope.  In this situation, you may need to turn down exposure to -1.5 to -2 to avoid the autoexposure circuit trying to make the shadow 18% gray while blowing out the bright areas.
8. Make sure to use the camera's diagonal to get the widest image possible for super wide angle and wider eyepieces.  You'll have to rotate the image in image processing software later.
9. I then proceed to take a series of 3 to 5 images to later pick out the best of the bunch on a large computer screen.  I've found that it's impossible to critically judge these images on the phone's screen.
10. I then take an angled image of the edge for super wide angle or wider eyepieces since the edge of field of even the best camera lenses is not as well corrected as the center.  It may also be cropped off for ultra wide field and wider eyepieces, so this is a necessity for them.
11. If your phone has an ultra wide angle camera, use it to take all-at-once images of ultra wide field and wider eyepieces.  I bought a second hand LG G5 phone for $25 off ebay just for its ultra wide angle camera since my S7 doesn't have one.  That's what I use to take my "full view" images.  I scale them up to match the scale in the center 20% of the S7 images.  Differences in angular magnification across each camera's field of view accounts for the slight width difference in the final images when using the same eyepiece.  Unfortunately, the G5's a 5 megapixel camera compared to the 12 megapixel S7 camera.  When combined with the smaller image scale, these "full view" images are pretty low resolution by comparison.  I'd love to acquire a 24 megapixel or higher ultra wide camera for this purpose.  Anyone know of used ones that sell for cheap on ebay?
12. In post-processing, I do not do any exposure adjustments or sharpening.  I just rotate and flip them to be more readable.  I also crop and composite them for comparison images.

[Don Pensack]

3 hours ago, Thalestris24 said:

Hi again

I suppose the main difference, visually, with a microscope that the view is almost just 2D so very little depth that's in focus (depending on objective power). In that case it's just rectilinear, chromatic and spherical distortion one wants to minimise. The spherical and chromatic distortions comes largely, if not wholly, from the objective (I think!). So for the EP it's really just the rectlinear distortion one wants to minimise though a small amount is still acceptable. One does want good contrast. It's like with engineering generally - good enough will do! The imaging side is naturally a bit more demanding but, even so, most of the time you end up cropping around the subject of interest which will likely be occupying the central area of the (objective's) fov. Still, having an EP with a largely flat field makes everything nicer and easier. At the end of the day, as with astro observing (which I've done very little of!), one just wants a pleasant experience   Oh, it's easy to 3D print appropriate adapters. For the EPs I can remove the 1.25" barrel from the astro EP and connect the optical part with the microscope via a 3d printed adapter (threads can be challenging and it usually takes me several goes before I get it just right!). The imaging train keeps the 1.25" barrel and connects via a1.25" astro helical focuser, and then a 3D printed adapter that connects it to the trinocular port. All seems to work ok  .

Louise

One thing: the 27mm EF eyepiece has about a 10% wider field stop than the 25mm Paradigm/Starguider.

That wider field could be a problem if there is any field curvature in the objective.

But Vlaiv's summary of why you might not want a telescope eyepiece for microscopy is relevant.

You should be looking at microscope eyepieces.  Yes, I know they cost more, but they are optimized for that usage.

Any telescope eyepiece will be a compromise.

[Don Pensack]

29 minutes ago, Louis D said:

First, does your scope use 23mm or 30mm barrelled eyepieces?  This is what ultimately limits the true field of view of any eyepiece in a microscope.  You can't see what's beyond the barrel.

Second, microscopes operate at high f-ratios (f/13+ as I understand it).  As such, they're not very demanding on eyepieces at the edges.

Third, I love my 23mm Aspherics in my binoviewer when barlowed to f/12 in my Dob or natively at f/12 in my 127 Mak.  It's super easy to get my nose between them and sink them deep into my eye sockets thanks to their diminutive size.  Being super light also makes scope balancing easy; although this isn't an issue for microscopy.

I also remembered I have unprocessed/unreleased 127 f/12 Mak images for several of the eyepieces I've mentioned here.  I whipped together a new composite image below for three of them.

As you can see, all perform really well at f/12 which is comparable to a microscope as compared to with the f/6 flattened ED refractor in the earlier image.

Though I notice that, par for the course, all have a fair amount of rectilinear distortion in the form of pincushion.  You could tolerate that in a microscope, but it wouldn't be preferable to an eyepiece with lass or none.

[Louis D]

There are many Chinese made, long eye relief, wide field (50 degrees in microscopy parlance) eyepieces on ebay for cheap that you might want to try.  They come in either 23mm or 30mm barrels already.

Edited February 22, 2021 by Louis D

[Louis D]

32 minutes ago, Don Pensack said:

Though I notice that, par for the course, all have a fair amount of rectilinear distortion in the form of pincushion.  You could tolerate that in a microscope, but it wouldn't be preferable to an eyepiece with lass or none.

For the binoviewer side of things, this won't matter as it is visual only.  Louise is looking for two, low cost, yet decently performing eyepieces for this purpose.

For the trinocular imaging side, she can probably stick with the BST she already has for now.  It seems to have the least distortion of the three in my image.  I don't think she's going to find a well corrected, budget, low distortion eyepiece that isn't a used Abbe orthoscopic.

I just remembered I had an image for a 25mm Abbe ortho for comparison sake, so I added it to the image, replacing the original image.  It does have lower distortion, but at the cost of a very narrow field of view.  Louis would need about a 33mm ortho to maximize the true field of view in a 23.2mm barrel.  The 32mm Tak Abbe orthoscopic costs £189.00 (with 20% VAT) new for reference.

Edited February 22, 2021 by Louis D

[Louis D]

1 hour ago, Thalestris24 said:

I'll wait and see what that Svbony aspheric is like

Remember to pull off the rubber eyecup if you need extra eye relief.  It's on a plastic barrel, so no worries about scratching your eyeglasses on the bare top.

The rubber eyecup can be quite difficult to work off the first time.  You may need to get a butter knife in the gap under it and work it around to pry it upward.

Edited February 22, 2021 by Louis D

[Thalestris24]

53 minutes ago, Louis D said:

First, does your scope use 23mm or 30mm barrelled eyepieces?  This is what ultimately limits the true field of view of any eyepiece in a microscope.  You can't see what's beyond the barrel.

Second, microscopes operate at high f-ratios (f/13+ as I understand it).  As such, they're not very demanding on eyepieces at the edges.

Third, I love my 23mm Aspherics in my binoviewer when barlowed to f/12 in my Dob or natively at f/12 in my 127 Mak.  It's super easy to get my nose between them and sink them deep into my eye sockets thanks to their diminutive size.  Being super light also makes scope balancing easy; although this isn't an issue for microscopy.

I also remembered I have unprocessed/unreleased 127 f/12 Mak images for several of the eyepieces I've mentioned here.  I whipped together a new composite image below for three of them.

As you can see, all perform really well at f/12 which is comparable to a microscope as compared to with the f/6 flattened ED refractor in the earlier image.

Hiya

The microscope does have 23.2mm eyepieces but I've made adapters to fit on the outside of the 23.2 recetacles. That allows me to get the whole 23.2mm diameter. The trinocular imaging path is slightly wider  As mentioned my oculars only give an 18mm fn. You can certainly buy 20 and 22mm ones for 23.2mm receptacles but greater than that normally requires 30mm eyepieces/receptacles. I'm waiting for a phone adapter to allow me to take the occasional images through the eyepieces though I use a dslr for more serious imaging.

Thanks for doing the above comparison - hmm... the Starguider looks better than the aspheric there? 

I think the 40x objectives (probably the one I use most often, but also 60x and 100x) work out at something like f/100 or greater. However, illumination is provided by bright LED

Louise

PS I should mention that my microscope only cost £216 new so it's not worth spending a lot of time, trouble and money on it. I am, though, a compulsive tinkerer

Edited February 22, 2021 by Thalestris24

[Louis D]

13 minutes ago, Thalestris24 said:

The microscope does have 23.2mm eyepieces but I've made adapters to fit on the outside of the 23.2 recetacles.

Clever woman you are. 👍

I tried a similar thing by slipping my 27mm Panoptic's 2" barrel over the 1.25" diagonal's eyepiece holder with the securing screw removed.  It worked great with little to no vignetting.  No wonder that it works so well.  With a 30.5mm field stop over a 31.75mm opening, there shouldn't be any issues.

[Louis D]

30 minutes ago, Thalestris24 said:

PS I should mention that my microscope only cost £216 new so it's not worth spending a lot of time, trouble and money on it. I am, though, a compulsive tinkerer

I've updated the comparison image with the addition of a 25mm Abbe ortho eyepiece.  Notice the lower distortion and narrower field of view.

Your best bet would be a 32mm Tak Abbe orthoscopic costing £189.00 (with 20% VAT) new for pristine images edge to edge.  This would nearly double the cost of your microscope, though.

[Thalestris24]

1 hour ago, Louis D said:

I've updated the comparison image with the addition of a 25mm Abbe ortho eyepiece.  Notice the lower distortion and narrower field of view.

Your best bet would be a 32mm Tak Abbe orthoscopic costing £189.00 (with 20% VAT) new for pristine images edge to edge.  This would nearly double the cost of your microscope, though.

Well, I'd need 2 of them...

[Louis D]

40 minutes ago, Thalestris24 said:

Well, I'd need 2 of them...

I was thinking of a single one for the trinocular tube to take low distortion, afocal images.  Distortion isn't all that important visually at the binocular viewer.

[Thalestris24]

8 minutes ago, Louis D said:

I was thinking of a single one for the trinocular tube to take low distortion, afocal images.  Distortion isn't all that important visually at the binocular viewer.

Ok, though the image quality using the Starguider have probably been good enough. Could always be better, I suppose. I'll dwell upon it

Oh, I previously posted some images of diatoms at 100x in the microscopy section:

 

Thanks

Louise

[Thalestris24]

PS it's almost essential to have the image train parfocal with the visual. It's also nice, but not quite so essential, to have the imaging fov the same as the visual  In the imaging train the 'eyepiece' is being used (afocally by me) as a projection lens, also called a photoeyepiece. Confusingly, advanced users often just call them eyepieces - for a long time I didn't understand what they were talking about!

Louise

[Louis D]

1 hour ago, Thalestris24 said:

PS it's almost essential to have the image train parfocal with the visual. It's also nice, but not quite so essential, to have the imaging fov the same as the visual

Once you have the binocular section focused, hopefully you can move the trinocular eyepiece up and down to reach parfocality and then lock it down as well.  You should also be able to focus the trinocular eyepiece using live view from the camera to a monitor screen.

[Thalestris24]

7 minutes ago, Louis D said:

Once you have the binocular section focused, hopefully you can move the trinocular eyepiece up and down to reach parfocality and then lock it down as well.  You should also be able to focus the trinocular eyepiece using live view from the camera to a monitor screen.

Yes, that's what I did - it's all set up. I've had it up and running with the kit eps and the Starguider for quite a while now

Louise

[Thalestris24]

10 hours ago, vlaiv said:

@Thalestris24

I can't help but wonder what are you doing exactly. Sorry if I'm being nosy, I'm just interested in "mechanics" of things - how do you plan to use equipment and to what effect.

You say that you need good eye relief EP - to be used by spectacle wearer but then you talk about flat field and afocal method.

My guess is that you are looking for all around EP for daytime use (digiscoping and observing of sorts) - but does it have to be single eyepiece?

You say that you need flat field EP, and that is ok, however, most of field curvature comes from telescope itself. For this reason, I'm guessing that you are using 80mm F/6 with field flattener - which also happens to be reducer (from your sig). You now have F/4.8 scope. There are very few eyepieces that will be corrected to the edge in such fast system and they are expensive.

For digiscoping - you just need certain field stop - focal length and AFOV are not as important as you can adjust things on camera side - by selection of lens on camera (or simply adjusting focal length in zoom lens). Maybe orthoscopic eyepiece would give best performance in this case even if it has narrow AFOV which might not be suitable for observation?

32mm GSO Plossl has as wide field stop as you can get in 1.25" format. Here is a test I did few days ago when I got my smart phone afocal adapter:

Or this one:

Both images are at 25% scale of original. Phone has 4000x3000 resolution but lens is such that it covers more than 50° of FOV so there is some black area in shot.

Btw this is 32mm F/4 achromat finder/guider scope. It is incredible little lens. Plossl fares quite well regardless of the speed of the lens.

Although this was hand held shot (I was holding complete contraption in my hand when I took this) - sharpness is still pretty good in the center of the field.  Pidgin is a bit out of focus because it is a bit further away. I think phone focused on branches in front of it.

Here is right edge - not looking bad at all

Left edge is worse - but it might have something to do with phone centering - I did not pay much attention how centered it is - and then there is out of focus due to distance blur:

 

Hi Vlaiv

I was wondering if you've done an astro imaging through the EP?

Louise

[vlaiv]

6 minutes ago, Thalestris24 said:

Hi Vlaiv

I was wondering if you've done an astro imaging through the EP?

Louise

Not yet, but I do intend to try - mostly EEVA style - both with phone camera and with dedicated astro camera (still need to get c mount lens for that).

I have this idea that Mak102 is great fast imaging scope when "properly" used - in this case afocal method like images I posted above.

Not going to use it for serious imaging but I do want to try out the approach - I think it is viable option for people just starting out and wanting to get their feet wet - low cost / all around scopes that can do both visual and imaging. Hope that phone adapter / afocal method and proper software support will deal with EEVA / basic imaging requirements.

[Thalestris24]

17 minutes ago, vlaiv said:

Not yet, but I do intend to try - mostly EEVA style - both with phone camera and with dedicated astro camera (still need to get c mount lens for that).

I have this idea that Mak102 is great fast imaging scope when "properly" used - in this case afocal method like images I posted above.

Not going to use it for serious imaging but I do want to try out the approach - I think it is viable option for people just starting out and wanting to get their feet wet - low cost / all around scopes that can do both visual and imaging. Hope that phone adapter / afocal method and proper software support will deal with EEVA / basic imaging requirements.

I've only ever used Sharpcap for eeva - I've no idea what might be available for phones. Do mention my name to alert me if you get anywhere!  I might have a go myself one of these days...

Thanks

Louise

[vlaiv]

1 minute ago, Thalestris24 said:

Do mention my name to alert me if you get anywhere!

Will do!

[Thalestris24]

Just a quick update. I received the aspheric EP today but it wasn't any good - wasted my money  I think, after all that, I'll just get another couple of the 25mm EDs.

Thanks all for the suggestions and data

Louise

[Louis D]

13 minutes ago, Thalestris24 said:

Just a quick update. I received the aspheric EP today but it wasn't any good - wasted my money  I think, after all that, I'll just get another couple of the 25mm EDs.

Thanks all for the suggestions and data

Louise

Sorry to hear that.  Mine have been excellent in binoviewers.  Perhaps they have gone down hill in quality over the last few years, or they are simply incompatible with the light cone of a microscope.

[Thalestris24]

12 minutes ago, Louis D said:

Sorry to hear that.  Mine have been excellent in binoviewers.  Perhaps they have gone down hill in quality over the last few years, or they are simply incompatible with the light cone of a microscope.

It may be just the microscope use. I've put it a 115mm frac so will have a look through in daytime, and night time - if we ever get a clear night!

Thanks

Louise

[Thalestris24]

22 hours ago, Louis D said:

Sorry to hear that.  Mine have been excellent in binoviewers.  Perhaps they have gone down hill in quality over the last few years, or they are simply incompatible with the light cone of a microscope.

Had a good view of the Moon with the aspheric on my 115mm/f6.95 frac and 2x Barlow  Shame I don't have my phone adapter yet! Should come next week, hopefully.

Louise