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Telescope Eyepiece Comparator


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http://scopecalc.grid-itc.com

I cobbled this together a couple of weeks ago, and have been populating it with data since. There are currently over 1400 eyepieces and over 400 scopes in the database. You can also add your scope manually if it isn't listed.

I'd appreciate any feedback, suggestions, more data, or if you think it sucks, tell me why!

Thanks,

- Andrew

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The eye piece calculator is great!

Very useful, thanks. :)

For example, I could not find the eye relief for the Baader Orthos anywhere on the net.

A possible improvement would be if you could list your Barlow lenses &c and have a list of magnifications for each eye piece; but its not exactly hard for me to work out x2 in my head :D.

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I'm glad you find it useful!

Don Pensack of Scope City was kind enough to furnish me with the eyepiece list which saved a massive amount of work. Some of the manufacturers simply don't release all the figures, so we either draw a blank, or make some attempt to calculate a rough estimate.

The Eye Relief on the Baader Ortho is only listed on the 5 & 12.5mm - data for the others is "N/A". I would have expected more from Baader, but they're not a large company, and when even the likes of Meade don't seem to release all the information (I have to estimate the field stop on all their EPs), you have to make the best you can with what you have!

I think I understand what you're talking about WRT multiple barlows. The problem I can see is data overload. It's not just the magnification that is recalculated. The TFoV, the exit pupil and the eye relief all need to be calculated and displayed for each barlow factor. I may change it so it can display the basic values + the barlowed value if it's set, but any more than that and I can see it becoming a huge wall of numbers! There's also a problem if your barlow is telecentric, because only the magnification should change, and none of the other values!

So many variables ... so little time :)

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I think it's a very useful tool - keeping up to date in the face of the constant flow of new products might be a challenge !.

My only suggestion would be possibly to re-label Total FoV as True FoV as that's what it tends to be known as as far as I'm aware.

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Not too much of a challenge! Not too many new EPs and scopes being developed. The database ... isn't! The whole thing runs from a couple of text files, so updates are very easy.

In the interests of saving space, I've relabelled with "AFoV" and "TFoV", with a popup giving a more detailed description when you hover over the description text.

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this is great! it works perfectly. a couple of well meant suggestions:

the Orion Optics UK 300mm is showing as f5.6 on the list nut changes to f5.3 on the spec. the latter is right the other presumably a typo?

it might be useful to have a 'powermate ratio' too as this would then reflect a more likely eye relief?

fabulous 'bit' of work! thanks for sharing it.

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Many thanks for all your kind words!

the Orion Optics UK 300mm is showing as f5.6 on the list nut changes to f5.3 on the spec. the latter is right the other presumably a typo?

Well spotted! Fixed that. Was a typo in the description.

it might be useful to have a 'powermate ratio' too as this would then reflect a more likely eye relief?

I was thinking about adding a "Telecentric" checkbox to the barlow calculation, which would then only affect the magnification and not all the other values. Also, to display both the base and "barlowed" values at once for barlow values other than 1 (no barlow).

It did indeed help! Thanks very much for that - filled in some gaps with a popular EP!

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A few small changes today.

Changed eyepiece display to show the current barlowed info as well as unbarlowed (in brackets), when the barlow factor is set to something other than 1x.

Added a "Telecentric" checkbox for those fortunate individuals with Powermates (only appears when you set a barlow factor other than 1x). This only affects the Mag and the TFoV - other parameters remain fixed with the eyepiece.

Lots of popups with information on each parameter - some of these items are quite difficult to pin down in a couple of sentences! I typed these in far too quickly over lunch, so if anything looks weird, doesn't make sense, or is complete gibberish, let me know! :)

Sorted the mobile friendlyness (cuts out the news, the links and the popups, and stacks everything vertically when it figures out that you're browsing with a phone - I've tested it fine with my E71 - once again, any problems, let me know).

Have fun with it!

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top job Andrew

my only complaint is that we can now see a (pretty much) complete list of eyepieces and scopes to slobber over and armed with all this data, we can justify anything (to ourselves - our other halves might be a different matter).

seriously good work and thanks again for your amazing turnaround of the suggestions just in the last 24 hours!

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  • 2 weeks later...

I've noticed that on the eyepiece comparator TeleVue Plossl apparent field of view ranges from 46-50 and Baader Planetarium Ortho's are all 47.

In the advertising guff for these lenses TeleVue claim 50 degree field of view and Baader claim 40 degree field of view.

What's going on?

Thanks,

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Interesting. I'm wondering if some of the figures are based on real-word measurement rather than the manufacturers figures. I took the eyepiece data as a spreadsheet - the source is trustworthy so I'm not sure ...

TeleVue list all the Plossls as 50 degrees other than the 40mm which is 43 degrees. I can't find anything to contradict this information, so either my source data is wrong, or somebody has measured the AFoV on these eyepieces accurately, or calculated it from the field stop. At this stage, I don't know.

The Baader orthos are weird. As you say, Baader quote 40 degrees. A good number of resellers quote 47 degrees. Google makes me suspect that neither number is accurate and the real values are between 41 and 43 degrees depending on focal length. What to do ... ?

I've changed the figures for the Televue Plossls and the Baader Orthos to the manufacturers figures. Can't really do anything else - if we can't trust the manufacturers data then there's no hope of making any good calculations.

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Hi Andrew,

Thank-you, great tool! It's in my bookmarks.

Seems that some items are missing though:-

Celestron C80 ED-R - Ap. = 3.2"/80mm, fL = 600mm, f/ = 7.5, max mag. = 160x

Meade (Series 4000) QX Wide Angle 30mm - fL = 30mm, aFOV = 70º, ER = ?, barrel = 2", field stop = ?

GSO/Revelation SV EPs -

fL = 26mm, aFOV = 70º
fL = 30mm, aFOV = 70º
fL = 42mm, aFOV = 65º
fL = 55mm, aFOV = 55º
ERs = ?, barrels = 2", field stops = ?

Re that wierdness with the Orthos, maybe there is some confusion because of the different types that are out there. My take on it is:

Baader Genuine Abbe Orthos == UO HD Orthos - aFOV all fLs = 40º, ERs = ?, barrels = 1.25", field stops = ?.

Circle T Orthos == UO Abbe Orthoscopic == various other volcano top Ortho brands -

4mm = 41°, ER = 3.5mm
5mm = 43º, ER = 4mm
6mm = 43°, ER = 4.8mm
7mm = 42º, ER = 5.6mm
9mm = 42°, ER = 7.2mm
12.5 = 44º, ER = 10mm
18mm = 46°, ER = 14.4mm
25mm = 47°, ER =20mm
barrels = 1.25", field stops = ?

(Info from Kokusai Kohki website, looks like Lyra Optic have mistakenly quoted the 0.965" sizes' aFOVs.)

Then to add to the muddle, the Vixen Circle V Orthos == Celestron Orthos - found no data for the aFOVs, etc.

HTH :D

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Hi Andrew,

Thank-you, great tool! It's in my bookmarks.

Glad you find it useful!

Seems that some items are missing though:-

Celestron C80 ED-R - Ap. = 3.2"/80mm, fL = 600mm, f/ = 7.5, max mag. = 160x

I'm filling in the scope details from the manufacturers websites. Most aren't interested in telling all about products which they aren't currently selling, so I'm reliant upon people to tell me what they have - thanks for the information. I've added the C80 to the list of scopes.

FYI, the only information I need is the name of the scope, the aperture, the focal length and the type of scope (especially with refractors - achromat, apo doublet, apo triplet, apo petzval, yadda yadda).

Meade (Series 4000) QX Wide Angle 30mm - fL = 30mm, aFOV = 70º, ER = ?, barrel = 2", field stop = ?

Odd that the 30 was missing. I found the eye relief data on optcorps website so I filled that in as well.

GSO/Revelation SV EPs -
fL = 26mm, aFOV = 70º
fL = 30mm, aFOV = 70º
fL = 42mm, aFOV = 65º
fL = 55mm, aFOV = 55º
ERs = ?, barrels = 2", field stops = ?
GSO seem to do a lot of badging. You can find all the GSO stuff under "Guan Sheng Optical (GSO)". I've added the superviews you have listed other than the 26mm as GSO don't have a 26mm "Superview"! They do have a 26mm "Super Wide Angle" with a 70 degree AFoV, so I suspect that Revelation are playing around with the branding. I've added those ones in with the eye relief figure I already have under a "Revelation (GSO)" heading. I'll have to have a look at the plossls as well because they aren't there.
Re that wierdness with the Orthos, maybe there is some confusion because of the different types that are out there. My take on it is:

Baader Genuine Abbe Orthos == UO HD Orthos - aFOV all fLs = 40º, ERs = ?, barrels = 1.25", field stops = ?.

Circle T Orthos == UO Abbe Orthoscopic == various other volcano top Ortho brands -

4mm = 41°, ER = 3.5mm
5mm = 43º, ER = 4mm
6mm = 43°, ER = 4.8mm
7mm = 42º, ER = 5.6mm
9mm = 42°, ER = 7.2mm
12.5 = 44º, ER = 10mm
18mm = 46°, ER = 14.4mm
25mm = 47°, ER =20mm
barrels = 1.25", field stops = ?

(Info from Kokusai Kohki website, looks like Lyra Optic have mistakenly quoted the 0.965" sizes' aFOVs.)

Then to add to the muddle, the Vixen Circle V Orthos == Celestron Orthos - found no data for the aFOVs, etc.

HTH :D

I think that those numbers you have for the Circle-Ts are probably the correct values for Orthos full stop. The ortho is a straightforward design EP, and anything which doesn't conform to that ain't an ortho!

Baader quote 40 degrees.

Our friends at FLO quote 40 degrees.

Harrisons quote 43 degrees.

Green Witch quote 47 degrees.

Sherwoods quote 47 degrees.

Telescope Planet quote 47 degrees.

RVO quote 47 degrees.

It's bonkers! :D I guess a lot of the resellers are quoting the widest figure possible depending on how you calculate the AFoV.

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Thanks! Really useful.

It would be possible to estimate the magnification achieved when using a modded webcam?

I have a lifecam, housed in an 10mm eyepiece, and by simple visual comparison, look like it achieve the same magnification as a 10mm plossl.

Cheers,

Martin

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It would be possible to estimate the magnification achieved when using a modded webcam?

Interesting idea. Would have to base it on the CCD chip in each camera. I'll add it to the "to do" list along with adding the zoom eyepieces which I haven't touched yet.

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  • 2 weeks later...

One of the often raised questions is will that work in an F5 scope (fast).

Is there any data that is factual on how far out from the centre of the FOV before you get say a star that is distorted to 1% of the FOV...

so a measure of field flatness..

So many of us seem to have these F5s and it woudl be useful..

Then add a buy it now link to a few sites and agree a commission and you can self fund the site...

Just some ramblings..sorry.

Mark

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One of the often raised questions is will that work in an F5 scope (fast).

Is there any data that is factual on how far out from the centre of the FOV before you get say a star that is distorted to 1% of the FOV...

so a measure of field flatness..

So many of us seem to have these F5s and it woudl be useful..

It's a great idea, but I have no data on it, and I suspect that no data would be forthcoming, or at least not enough to make it useful.

It's more to do with the design of the eyepiece than anything else.

I would suspect that only premium manufacturers - TeleVue, Pentax, Vernonscope, Burgess, Baader, some of the higher quality Meade and Celestron gear would be interested in releasing this information. Given the sparse information most of these guys already issue (Meade and Baader, I'm lookin' at YOU!), it's going to be very tough to get anything out of anybody but TeleVue.

Lower quality stuff, and I rekon they would much rather stick with non-specific marketingisms rather than hard facts.

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