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APM / Lunt 5mm: 5mm or 4.7mm focal length

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#1 blueflash

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Posted 07 September 2018 - 02:33 AM

Hello every one.

 

This is my first post here, but I read a lot on the forum.

 

I have a short question concerning the apm / lunt 5mm 110 eyepiece. I read several time on this forum that this eyepiece has actually a focal length of 4.7 mm (or even 4.77 mm). I searched on the internet but never find any source / specification that confirm this.

Now, I don't think that this really matters as I would probably not see any difference between 4.7 and 5mm. But I am still wondering if it is a 5 mm or a 4.7 mm eyepiece. ;)

Do someone know which focal length the eyepieces actually has?

 

Thank you.

 

 

 



#2 havasman

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Posted 07 September 2018 - 03:22 AM

Hi blueflash & welcome to the forums!

 

You might ask Markus at APM. He could certainly tell you. They list it as 5mm focal length on their spec sheet. 

I recall the William Optics XWA was 4.77mm as were the others of that vintage (Myriad, Stellarview, etc.) but I have also not seen the APM so noted.



#3 Starman1

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Posted 07 September 2018 - 01:13 PM

Hello every one.

 

This is my first post here, but I read a lot on the forum.

 

I have a short question concerning the apm / lunt 5mm 110 eyepiece. I read several time on this forum that this eyepiece has actually a focal length of 4.7 mm (or even 4.77 mm). I searched on the internet but never find any source / specification that confirm this.

Now, I don't think that this really matters as I would probably not see any difference between 4.7 and 5mm. But I am still wondering if it is a 5 mm or a 4.7 mm eyepiece. wink.gif

Do someone know which focal length the eyepieces actually has?

 

Thank you.

Unless they changed the optical configuration, it's probably 4.77mm.

For what it's worth, marketing departments will often round off to make it simpler to advertise and sell the eyepiece.

For example, the old pseudo Masuyama eyepiece sold in the early '90s as a 3.8mm eyepiece was really 3.75mm and they simply rounded off.

Today, most sellers would call a 4.77mm eyepiece a 4.8mm.

But, perhaps that was the design spec and the production came out closer to 5mm.  Had it been 4.95mm or 5.05mm, I could see selling it as a 5mm.

Production specs are often a little different than design specs, but very rarely more than 0.1mm different.

So is it 4.77mm or 5mm?  It's fair to consider it a 5mm eyepiece until a lab test shows something different.

I compared it to a 4.7mm TeleVue Ethos SX and could see no difference in magnification, but then, the difference would be between 383x and 365x in my scope and I couldn't reliably see a difference of less than 5% at that magnification.

And who's to say the Ethos SX is exactly 4.7mm?

 

I'll agree with Dick--ask Markus Ludes about it.  I'd bet he knows the complete history of the eyepiece.



#4 blueflash

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Posted 08 September 2018 - 04:30 AM

Thank you very much for yours detailed explanations!

I just asked Markus Ludes. As soon as I have an answer I will let you know if this it a 5 mm or a 4.77 mm eyespiece ;)



#5 blueflash

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Posted 09 September 2018 - 12:43 PM

Markus Ludes replied to my message. => United Optics confirmed that this is a 4.7 mm eyepieces.

ps: this also means for me that there is plenty of space between my Ethos 8mm and my Lunt 4.7mm for a 6mm.. ;)

#6 Starman1

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Posted 09 September 2018 - 12:46 PM

KUO, huh?

That confirms my suspicion.

And it means the New Meade 82°s are from the same factory.

Interesting.  I guess I'll have to change my website.

Don



#7 blueflash

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Posted 09 September 2018 - 01:17 PM

He wrote "United Optics". So I think that is KUO, but I am not sure.

#8 Starman1

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Posted 09 September 2018 - 01:22 PM

KunMing United Optics is often referred to as United Optics.



#9 Galosimo

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Posted 10 September 2018 - 10:26 AM

hi starman, did you find any difference between apm and ethos sx?



#10 Starman1

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Posted 10 September 2018 - 10:49 AM

I haven't done any deep comparison between the Ethos and APM in this focal length.

I have used it briefly in my 4" refractor and the image quality is fine, but I did not really examine all its parameters.

I'm going to spend some time with the whole set in November at a 3 night star party.


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#11 Galosimo

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Posted 11 September 2018 - 12:34 AM

I hope I will soon have a comparison between the 2. I am very curious. The only thing that hampers the purchase of the 5 mm is the price too low compared to an ethos or eyepiece of excellent workmanship.



#12 Ryan555_1

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Posted 30 October 2018 - 02:04 PM

I haven't done any deep comparison between the Ethos and APM in this focal length.

I have used it briefly in my 4" refractor and the image quality is fine, but I did not really examine all its parameters.

I'm going to spend some time with the whole set in November at a 3 night star party.

I look forward to the comparison!

 

I have only compared informally thus far, and my APM/Lunts measure up very well to my Delos. In fact, I cannot tell any real difference in contrast and color between my 9mm APM and 10mm Delos except for FOV and magnification. (The APM also have some ghosting reflection at that focal length.) If anything, my wife and I preferred the color rendition of the APM over the Delos on Saturn. The yellow really popped, but then again that could be the magnification difference. 



#13 Spartinix

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Posted 30 October 2018 - 05:04 PM

I have done some comparising between an APM13 and Ethos13 (matching FL's) and I found the APM's to be very, very close to the Ethos. As I said before (not sure on CN or elsewhere); one would really expect for TV to be at least a little better overall than APM (tough not in all areas) to justify the much higher price. I want to stress however, that this comparing was done with F5 systems of rather unknown optical quality. Though one could definitely say, for most people, on average, for F5 systems, APM is about just as good, especially when factoring in price.

I've held on to the Ethos for now, because it came my way at a real good secondhand price and because I can afford it at this time, but I could be very happy with APM all the way I'm sure. I think, in my limited experience, that differences are noticed in comparison primarily and that one has to be quite occupied with excellent optics in general, as opposed to only enjoy observing in general.

Nevertheless, I have the greatest respect for Televue, as no doubt, being the best for systems of F10 down to F2.x.




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