Ruud

Hi,

I've repaired my formula and now I get amazingly exact results. Baader certainly provides the effective field stop diameters, rather than the dimensions of the front lenses.

Here's a screenshot of the field stop results I get with the new formula, compared with the values Baader gives.

See how the field stop of the 4.5 mm is calculated with a precision of 0.01mm?

Attached you find a short pdf document which explains the two formulas I used: one to calculate pincushion distortion (the Morpheus have 15.1% of it), and another to calculate field stops.

Both formulas are very easy! Have a go and read the pdf. It will take no more than a minute or two.

The pdf: FS SGL.pdf

Meanwhile I'm very happy with the 6.5 mm. I've even decided that I have an eyepiece gap in the 17.5 mm range.

Bye!

Ruud,

Can you show your formula for calculation field stops? How do you estimate how much Rectilinear in an eyepice? I mean in term of measurement, not the calculated geometrical distortion.

For eyepieces I just look at straight lines to estimate rectilinear distortion (RD). Some have a lot for their afov (panoptics, my Nagler 4.8), others seem to have very little (Delos). RD in eyepieces is always of the pincushion type. I've read that correcting for pincushion distortion increases astigmatism which would explain why so many eyepiece designs allow for it.

Measuring RD is difficult because angular magnification distortion (AMD) can be present as well. With AMD, the magnification (focal length) of the eyepiece varies from the centre to the edge of the field. If AMD is of the barrel type, the image looks like it is pasted on the outside of a sphere, and if the AMD is of the pincushion type the image looks pasted on the inside of a sphere.

Measuring distortion for camera lenses is easy. To undistort images from camera lenses you can use Adobe Camera Raw (expensive and not always successful) or Hugin panorama stitcher (free and it always works). The settings of the parameters in both programs would give you a reproducible measurement of the distortions present in the original images. There's a guy at ESA who uses Huging for just that purpose.

My formula to calculate field stops is empirical. I just tried lots of variations with tangents. Here's a screenshot with some comments, and below it is the worksheet itself, if you want to try it:

ScopeCalculator11 .xls  (Please see post number 46 for corrected version of this spreadsheet)

By the way, I read that the afovs of some of the Delos are smaller than 72°, and that the afovs of the Hyperions are larger than 68°.

Now, if the avofs of the Morpheus are slightly bigger than the stated 76°, my field stop errors are as I've come to expect them from the worksheet. In my 500 mm fl telescope it takes a star at the equator just 240 seconds to travel across a 8.75 mm field stop. I'll need no more 15 minutes of clear sky and I can do the drift test three times. 

Got the 6.5 mm Morpheus!

and it's every bit as good as Bill describes. What a nice eyepiece!

That's an amazing collection of cases, Dave.

We need more pictures, in which you open them all, case after case.

Hi Andrew, 

the slowly moving stars are satellites. The most obvious are the International Space Station and the Iridium satellites. The Iridium satellites can show very bright reflections of sunlight, and for the ISS you can subscribe to the Spot the Station service of NASA.

Lovely case everyone. With such well protected and cared after eyepieces, I would not hesitate buying second hand from any of you.

A wonderful instrument. Congratulations, Alan!

Hi all,

we're close to a hundred pages now. Does anyone else think it would be a good idea to start a new thread "Show us your eyepiece case(s) part 2" ?

Cheers

Problem solved, and a great solution it is.

Hi, I wonder if the observation is incompatible with a quad copter or a Chinese lantern.

Olly, Tim, it's magnificent !

Thank you for putting so much work in it. What an accomplishment !

Ah, thanks.

my new case with only a few select eps. i wonder how many times i have done this. last one now

You certainly are a master in the art of foam cutting, and yours is a wonderful case with beautiful eyepieces, but what is that thing at the bottom? 

You'll need more than one case...

Hello Vlad,

You clearly have an eye for quality. Please tell us, why do you have your mind set on both a 24mm Panoptic and a 22mm Nagler?

Nitrogen, Argon, it doesn't matter -- It's a gimmick anyway.

Argon is used in light bulbs. It must be quite inexpensive.

I got rid of my Explore Scientific 100 degree EPs, I like the Televues better in my Dobs. I tend to use the 10mm Ethos and Paracorr II most of the time. The cases were made by Ron Burrows at Wood Wonders in the US http://www.wood-wonders.com/

Beautiful cases, Barry, and a wonderful collection of glass. I enjoyed looking around at Wood Wonders' website. 

This is my final collection, my wife's words........

Hi Trazor, you have some great eyepieces in your collection and you're obviously more dexterous than most of us with pluck foam. Neat job!

Vixen says 65° on their website. That's what GotGazer 's says on the barrel, but Michael's says 72°.

You'd think that Vixen reduced the afov without changing the name of the eyepiece. That's confusing!!

Pincushion plays a role in how big the true fov is. The 10 mm 90° Takahashi UW (the king of pincushion distortion) has a bout the same true field as the 10 mm 82° Celestron Luminous.

Great eyepieces, Bond19, but the pluck foam doesn't do them justice. I've heard that you can use fretsaw on deep-frozen foam to get nicely fitting holes with good looking edges (maybe the foam needs to be moist for that). I'm planning on trying this myself.

It's a terrific arrangement, YKSE.  You spent those cloudy nights well. And your money too - nice eyepieces!

It's a beautiful collection, Steve. Nice case too!

Plantins!

Isn't that €8000 worth of eyepieces?

Go and see a shrink!

I'm kidding, and green with envy. I think your collection is awesome.

Wow! $150!

It's beyond my budget for cases, but it still looks nice.