Maximum Magnification for the Moon

[Splodger]

Hi, the theoretical max magnification for my scope according to astronomytools.com is 375x - 150 x 2.5. I’ve surpassed that on a few occasions but only with very good seeing. I’ve just got a new zoom eyepiece which together with a Barlow will easily allow much higher magnification. When the skies up here in Oregon eventually clear I’ll be out observing the moon. Will I be able to achieve greater magnification while observing the moon? Does it make any difference that the moon is only a hop, skip and a jump away? Thanks 

[Stu]

Which scope do you have @Splodger? The Moon is a very high contrast object and takes magnification well, so it’s often all down to the skies. If the Moon is high (as it is now), and the seeing is excellent then you can chuck quite a lot at it. Observing is not all about magnification though, so make sure the views are still sharp; don’t push it just for the sake of it.

[Ian McCallum]

I've got an 8" Dobsonian and have used 375x magnification on the moon, very occasionally. Even with a F6 ratio on the telescope, I can tell you that at those magnification levels, the moon is very dim and you will probably see 'floaters' in your view.  Contrast is very low too, even on a bright moon!

[Mr Spock]

x375 is certainly too much for a 150mm. All you are doing is making things larger and dimmer. You won't see any more detail.

It depends on scopes and seeing conditions, but with my 250mm for lunar x300 is about right; my 102mm refractor can hold x200 pretty well, though it just makes things larger above x100.

I believe the formula for 20/20 vision is x0.5 per mm for resolving fine detail, above which things are just made larger. My experience is x1 per mm is more comfortable for seeing fine detail.

[johninderby]

As mentioned it all depends on the scope and the quality of the eyepiece. I have used 700+ mag on the moon under perfect seeing without the image getting too dim but it takes a good scope to do so. Most of the time I use lower mag and just use the high mag to tease out fine detail.

[ollypenrice]

To get a good idea of the problem you could try looking through your scope at some distant text. This won't give you an idea of your maximum useful magnification on the moon but it will demonstrate that, beyond a certain point, the enlarged image contains no new information and may, through loss of contrast, contain less. Try reading the letters backwards to prevent the brain from anticipating them.

The only time 'excessive' magnification can be useful is in splitting doubles where the idea is not to get a good crisp view of the star but to try to see if it's a double or not.

Personally, I think that staying at the eyepiece, concentrating and awaiting those precious moments of good seeing, will give you an experience of more lunar detail than you'll get by swapping eyepieces.

Olly

[Roy Challen]

I fully understand, and agree with, everything posted above. Yet, I had one session in 2021 that had the best seeing I've ever experienced in this country. Looking at the Moon with my Tal 100 achro, I used a 6mm plus x2.25 barlow, giving x375. If I'd had higher mags at my disposal, I would have used them.

I do understand that I didn't see anything extra that half the magnification would've shown, but what I did see was bigger, therefore easier on the eye. I didn't have floaters (which is unusual for me) and the image was acceptably bright.

My conclusion is that maximum magnification is as much dependent on seeing conditions as it is on optical theory and quality. It may also be dependent on the lunar phase - somewhere halfway between new and full seems to be best.

[John]

The seeing conditions have to co-operate to make using very high magnifications on any target worthwhile.

While it is not the highest magnification that I've used, if the seeing is steady then I often find that 300x-350x seems to give me the optimum balance of image scale, sharpness and contrast when using my 12 inch dobsonian for lunar observing.

When I use more I usually find that seeing the finest details (eg: the smaller Plato craterlets, the central rille in the Vallis Alpes, small crater chains, floor markings in the Messier craters etc, etc) actually become harder to pick out, despite the larger image scale. 

So it's about getting the balance right and judging what the seeing will make worthwhile I think. Some experimenting is always fun as well

 

Edited January 2, 2022 by John

[Splodger]

8 hours ago, Stu said:

Which scope do you have @Splodger? The Moon is a very high contrast object and takes magnification well, so it’s often all down to the skies. If the Moon is high (as it is now), and the seeing is excellent then you can chuck quite a lot at it. Observing is not all about magnification though, so make sure the views are still sharp; don’t push it just for the sake of it.

I have a Meade LX85 150mm Mak. As mentioned above, the only time I have been able to get very high magnification was with a friends ES 5.5mm splitting doubles. Doing my maths now I can see that I wasn’t even close to 375x, but it wasn’t particularly difficult to focus and see differences of colour with that gear. The highest magnification combination that I have had with my own equipment is 200x.  That with my 18mm Meade and 2x Barlow. 
 

The new eyepiece is a Baader 8-24mm zoom. I ordered it with a 2.25x Barlow. It so happens that I’m sending the kit back to B&H today and replacing it with the eyepiece alone as I have the 2x already. My thinking was that with that eyepiece and Barlow I could get much greater magnifications. I see now my expectations were unrealistic. 
 

Even so, extrapolating from what I have read above, the 8-24 zoom and Barlow combination will allow me the greatest magnification I can realistically achieve under any viable seeing conditions. I’m pleased with that. And pleased that After reading the comments above I won’t be disappointed at the eyepiece. 

Edited January 2, 2022 by Splodger
Spelling

[Franklin]

The Baader MkIV zoom is a fantastic piece of kit and the good thing about using it, with or without the barlow, is that you can dial in the correct magnification for the object and the seeing at that time. It's a lot easier trying to gauge the correct power for the night when you don't have to keep interupting your observation by swapping out eyepieces. Once optimum power is found, you can always swap out for an appropriate fixed focal length eyepiece if you wanted to.

[Pete Presland]

I seldom find the conditions allow me to go above X300 with my C9.25, i am happy with the balance between brightness and detail this gives me. 

[Mr Spock]

3 minutes ago, Pete Presland said:

I seldom find the conditions allow me to go above X300 with my C9.25, i am happy with the balance between brightness and detail this gives me. 

When I had a C9.25 I found on the moon the 8mm LVW was my best eyepiece - x294. Nice and crisp at that with good contrast.

[Deadlake]

I find when magnification gets up to near 400-500x if seeing allows its the mount that takes over. In this case I like to use a goto mount to move the scope over the moon, then only focusing will create wobbles in the view. 

[Splodger]

2 hours ago, Franklin said:

The Baader MkIV zoom is a fantastic piece of kit and the good thing about using it, with or without the barlow, is that you can dial in the correct magnification for the object and the seeing at that time. It's a lot easier trying to gauge the correct power for the night when you don't have to keep interupting your observation by swapping out eyepieces. Once optimum power is found, you can always swap out for an appropriate fixed focal length eyepiece if you wanted to.

I was thinking along those lines. More time at the eyepiece. Also I’m a bit clumsy. The less swapping out I have to do the better

[Franklin]

17 minutes ago, Splodger said:

I was thinking along those lines. More time at the eyepiece. Also I’m a bit clumsy. The less swapping out I have to do the better

Exactly, you don't need to be clumsy, it's dark out there! I've got a case full of eyepieces and some of them are quite up there with the best, but the Baader zoom still gets used the most. I call it lazy stargazing, a low power/widefield eyepiece, zoom and barlow and maybe a couple of filters depending on what I'm trying to see and at the moment that's mainly cirrus, stratus and cumulus nimbus!😭

[Splodger]

1 hour ago, Franklin said:

Exactly, you don't need to be clumsy, it's dark out there! I've got a case full of eyepieces and some of them are quite up there with the best, but the Baader zoom still gets used the most. I call it lazy stargazing, a low power/widefield eyepiece, zoom and barlow and maybe a couple of filters depending on what I'm trying to see and at the moment that's mainly cirrus, stratus and cumulus nimbus!😭

That brings to mine another question regarding Wide Field Low Power eyepieces but I think a new topic is in order - Low Power  Wide Angle  Inexpensive  Eyepiece for my Mak? Ha! I should be so lucky!

[Franklin]

On 02/01/2022 at 23:33, Splodger said:

Ha! I should be so lucky!

Yes, you've got quite a lot of focal length with the mak. Secondhand WO 2" 40mm Swan? 1.55deg at 45x, but probably best you can do without having to get a second mortgage!

Edited January 4, 2022 by Franklin
correction