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What do you think delite 3mm for a 8" dob?

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#1 cnchillstar

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Posted 23 July 2021 - 08:55 PM

For a 8" F6 orion dob and ES 6" F8 refractor, I would like to do some serious moon and planet watching. Is a delite 3mm ok? If not please give some options thanks.


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#2 CrazyPanda

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Posted 23 July 2021 - 09:05 PM

400x is going to require dead calm atmospheric conditions, and assuming the refractor is achromatic, you're basically just going to be magnifying chromatic aberration in the refractor and it's just not going to look good. A 3mm DeLite would be a waste of money in the refractor.

 

Do you know for a fact that your skies are steady enough to use 400x?



#3 Barlowbill

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Posted 23 July 2021 - 09:07 PM

I have used a 3.2mm Astro -Tech Paradigm for a couple of years.  About 4 times.  Pretty high power for my 8" Dob.  I like it and will not get rid of it but it is a few and far between usable ep.  



#4 sportsmed

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Posted 23 July 2021 - 09:41 PM

I have a 10" Dob and a 3mm is just too much, honestly for higher mag I wouldnt try to go much more then a 5mm on alot of nights and a 6-7mm would get used more for sure. You would have to have some great calm dark skies for you to get much use of a 3mm. Delites are nice but I wouldnt waste money on the 3mm instead spend on a 5 - 7mm for higher power.


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#5 Bill Jensen

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Posted 23 July 2021 - 09:52 PM

I enjoy my 3-6mm Nagler. It gives me a range depending on the seeing when I am pushing the limits of the sky for a particular night. They come up on the used market from time to time as well 


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#6 ngc7319_20

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Posted 23 July 2021 - 10:03 PM

As others have said, get something in the 5mm - 6mm range.  And then if you feel you still need more power, try something around 4mm.    I hardly ever use a 3mm.

 

Another point is that the field of view will be very small at 3mm, making it difficult to find objects and track them.



#7 SkyRanger

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Posted 23 July 2021 - 10:12 PM

My most used lunar and planetary EP in my 8” f/6 was an 8mm.  Shorter focal lengths were used far less frequently.  If you have consistently great seeing, you can use higher powers more often.

 

Gordon G


Edited by SkyRanger, 24 July 2021 - 05:22 AM.

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#8 Barlowbill

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Posted 23 July 2021 - 10:23 PM

I agree with everything that has been said.  However, in those infrequent times that allow more power, more power is fun.  I would not spend $ on high end eps for those infrequent tines.



#9 TOMDEY

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Posted 23 July 2021 - 10:33 PM

Well, that's a miniscule exit pupil. I know some people go that high (50-60x per inch of aperture) but think it also relates to one's visual acuity. If your eye's are getting kinda weak (corrected acuity 20/30 or worse) the extra magnification might help. In that case, the dinky exit pupil can avoid most of the lumps and bumps in your eye's wavefront. Whatever works for you is best! When I got my eyes fixed, I discovered that much lower magnifications now feel optimum.    Tom



#10 Napp

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Posted 23 July 2021 - 10:40 PM

Are you willing to spend that much for an eyepiece you may only use once or twice a year if you are lucky.


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#11 Astro-Master

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Posted 23 July 2021 - 11:03 PM

A good quality Barlow works well on all my scopes.


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#12 Dave Mitsky

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Posted 23 July 2021 - 11:20 PM

I doubt that you will be able to use 400x very often, if ever.  A 0.5mm exit pupil (3mm/5.9) is going to produce a rather dim image and will probably result in "floaters" in the vitreous humor being an obvious nuisance.


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#13 The Ardent

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Posted 23 July 2021 - 11:23 PM

For “serious moon and planet watching” I recommend a binoviewer. 
 

I really wish you had been at Neaf 2017 when I left the hotel and drove back to Neaf after dark, and set up my 120mm refractor, BV and pairs of 11mm and 18mm Delites , and watched Jupiter low in the east. There were a couple of other astronomers there for night viewing too. I didn’t stay long because of driving all the day before, little sleep, then a full day of solar observing and shopping. 

 

What did the BV do? It showed me a better Jupiter than any single eyepiece. 

If you had been there, and seen it for yourself , it would make a lot more sense than any explanation I can write. 
 

Or do this , walk around the house and do your daily living (no driving or operating machinery) with one eye closed. If that works for you, then don’t consider a BV. 



#14 RichA

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Posted 23 July 2021 - 11:50 PM

For a 8" F6 orion dob and ES 6" F8 refractor, I would like to do some serious moon and planet watching. Is a delite 3mm ok? If not please give some options thanks.

Used to be, people would wait 1/2 a night for that fleeting few seconds of extra steadiness when powers of 50x or more per inch (assuming their scopes would support it) would be of benefit when looking at planets.  Also, using such powers on things like the heart of the Orion nebula or a small planetary nebula would be interesting.  But stars in a six-inch at become diffraction images, little spheres with rings around them.  The point at which you can see them clearly is the limit of the resolution of your scope.  Going beyond the power needed to see them may be more comfortable for things like very close double stars.



#15 cnchillstar

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Posted 24 July 2021 - 05:48 PM

Thanks for every reply!  I will cancel 3mm, and keep using my Monpheus 6mm. 


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#16 Tropobob

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Posted 24 July 2021 - 07:46 PM

Thanks for every reply!  I will cancel 3mm, and keep using my Monpheus 6mm. 

The shortie barlow works well with my 12.5mm Morpheus. On nights of good seeing, I have sometimes used two such barlows and still had a very good image. A barlow is a lot cheaper than a new EP, although, I expect that there will be many evenings when 400x is just too much for the conditions.  

 

Pictured: My Tak 100mm, with the 12.5mm Morpheus and two barlows. 

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#17 Jon Isaacs

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Posted 25 July 2021 - 04:55 AM

Thanks for every reply!  I will cancel 3mm, and keep using my Monpheus 6mm. 

ifwhether a 3mm focal length would be useful.  In most places, it probably would not get a lot of use but where I am located, the seeing is often quite good so I will use my 3.5 mm Nagler on a nightly basis and on many nights I will use it with a 2X Barlow.  

 

But the first step is a good Barlow, that can cover your needs for a good short focal length eyepiece for those extra special nights.  If you need more than the Barlow plus your 6mm Morpheus provides, that's the time to think about a shorter focal length eyepiece.

 

Jon



#18 earlyriser

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Posted 25 July 2021 - 05:10 AM

For planet viewing, I’d want an eyepiece that could get me to 300-400x on an 8 inch scope.  I’d also want a scope that tracks, but that’s another story.  

 

Even with less than perfect seeing during the last Mars opposition, I experienced brief moments when the image really cleared up. However, my highest power eyepiece spends most of its time in the eyepiece case. I use it maybe 1% of the time. But I also don’t do a lot of planet viewing. 


Edited by earlyriser, 25 July 2021 - 05:18 AM.


#19 Simoes Pedro

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Posted 25 July 2021 - 09:42 AM

For a 8" F6 orion dob and ES 6" F8 refractor, I would like to do some serious moon and planet watching. Is a delite 3mm ok? If not please give some options thanks.

For moon and planets it tend to prefer 0.66 to .75 exit pupil, and I am positively sure 0.50 is way too much. Too find exit pupil just divide eyepiece focal length by F ratio.

 

Planetary magnification is a tricky business. You need sufficient magnification to be able to see the features, while at the same time still having decent contrast.

 

I common mistake is to believe you need .33 to .50 mm to really reach the maximum resolution of the instrument (50 to 75x/in). This is far from the truth.

 

Based on the my experienced with the Q3.5, with 16mm I can see almost the same detail as with a 12 mm eyepiece. The difference being that image brightness and contrast is much better. 

 

In conclusion, my advice is to fine tune maximum planetary resolution by trail and error. If you do not have a chance to play around with different focal lengths, pick an eyepiece in the 0.66 to 0.75 mm range. For your two scopes (F6 and F8), I bet would be on the 5 mm delite.


Edited by Simoes Pedro, 25 July 2021 - 09:43 AM.


#20 N3p

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Posted 25 July 2021 - 10:05 AM

Thanks for every reply!  I will cancel 3mm, and keep using my Monpheus 6mm. 

I was about to say that, a 6mm is what I use for the moon almost all the time, I have more powerful options available but I rarely use them. My telescope is 200mmx1000fl and the sweetspot on the moon is around 170x. (167x) 1.2mm of exit pupil, I get almost no floaters with a exit pupil like that.

 

I see a degradation in resolution most of the time just by switching to a 5mm. the 6mm It's enough for serious moon observation within the limits of that aperture, with my lovely 6mm Delos it's as good as it can be.



#21 Frenchy

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Posted 26 July 2021 - 03:42 PM

There may be nights it could be useful, but they will probably be few and far between. Exceptional seeing can be pretty rare depending where you are located. Reason I say it "could" be useful is because I had a night last week when I was looking at the moon and kept increasing mag and kept waiting for it to look like a hot mess. It never did and I got up to using 5mm nagler with 1.5x magic dakin barlow which is equivalent to a 3.33mm and with my 12" dob it yielded 457x. I've never seen the moon that sharp and close through any of my scopes ever. Been viewing from my house for 3 yrs and can only count 1 other night in that span that had similar sky conditions. Will I likely be able to pull that off again soon? Probably not. But having a good high power option to me isn't a waste. 




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