90x Per Inch!!...How?

[jetstream]

6 hours ago, chiltonstar said:

A large, high resolution scope will broaden the feature a little but not degrade too much the intensity of the feature, but a small scope with low resolution will broaden the feature a lot and reduce its intensity a lot.

Excellent explanation Chris and thanks for it. I have never heard of the effect of aperture explained in this way and it makes sense, sense of something I've been wondering about for years.

Once again contrast is a huge factor in telescope performance.

[John]

2 hours ago, markse68 said:

You maybe get more patience though to partially compensate? 

Mmmm - not sure about that !

 

[Stu]

One thing I have noticed is that doubles can be surprisingly easier than you might expect in small aperture scopes. My understanding of airy disk size in relation to aperture has certainly improved over the last year.

The small scopes produce much larger airy disks than larger scopes, which means they are much easier to see and so doubles actually look nicer in some ways as they look more like bullseyes on black. In a larger scope, often the much smaller airy disk is lost in diffraction spikes or thermal currents, so they look much messier.

Of course, ultimately a good big scope will resolve tighter doubles than a good little scope, but seeing and cooling effects often mean the smaller ones appear to perform better (within their resolution limits). Aesthetically I certainly enjoy seeing those bullseyes, and conversely don’t particularly enjoy trying to spot a tiny spec of light next to a big blurry star (eg Sirius), somehow it just doesn’t float my boat.

[andrew s]

42 minutes ago, Stu said:

One thing I have noticed is that doubles can be surprisingly easier than you might expect in small aperture scopes. My understanding of airy disk size in relation to aperture has certainly improved over the last year.

The small scopes produce much larger airy disks than larger scopes, which means they are much easier to see and so doubles actually look nicer in some ways as they look more like bullseyes on black. In a larger scope, often the much smaller airy disk is lost in diffraction spikes or thermal currents, so they look much messier.

Of course, ultimately a good big scope will resolve tighter doubles than a good little scope, but seeing and cooling effects often mean the smaller ones appear to perform better (within their resolution limits). Aesthetically I certainly enjoy seeing those bullseyes, and conversely don’t particularly enjoy trying to spot a tiny spec of light next to a big blurry star (eg Sirius), somehow it just doesn’t float my boat.

I think that  captures the reason why "small" refractors have such a strong following. Couple that with ease of use and stable collimation then you have a winner. Especially  with modern examples with little or no chromatic aberration. 

Regards Andrew 

PS I still prefer reflectors. 😜

Edited August 14, 2020 by andrew s

[chiltonstar]

14 hours ago, andrew s said:

 

PS I still prefer reflectors. 😜

Therapy, or buying another scope can cure this addiction.😼

Chris

[johninderby]

6 minutes ago, chiltonstar said:

 buying another scope can cure this addiction.😼

Chris

But for how long. A week or two maybe? 😁😁😁

[Tenor Viol]

I think we all realise that you need exceptional seeing conditions to be able to use high magnifications. There are few subjects it suits anyway - Moon is probably the primary one and the planets. 

I'm sure in the old days in books I was reading as a novice back in the 70s and 80s (so Sidgwick, Moore et al....) used to quote 100x per inch for refractors. In reality, 50x per inch is probably the best that you can do on a 'good' night. Occasions when you could use more are very rare in the UK because of generally high level of aerosols, humidity etc. But it varies, I am sure those living in dry arid climates have more opportunities to use higher powers than is generally feasible in the UK.  

[John]

I've bought a couple of really cheap scopes over the past couple of months and those have proved a lot of fun for very little outlay.

In many ways it's more satisfying getting some nice views from a £50 scope than it is pushing a £2000+ scope to it's limits

 

 

[Stu]

1 hour ago, John said:

In many ways it's more satisfying getting some nice views from a £50 scope than it is pushing a £2000+ scope to it's limits

I’ve held that view for quite some time John as you may know. I reckon trying to spot GRS or a shadow transit, or split a tight double is just as challenging in my 65mm TAL Alkor for example as spotting a mag 15 galaxy in a 20” dob under pristine skies. Both of them improve your observing skills and are very rewarding.

I still need to try my ‘Cheapest Double Double’ challenge. Some time back I bought three battered old 60mm long focal length (f16?) achros for a grand total of £15 off eBay. I want to see if I can split the Double Double with one (or more) of them.

[andrew s]

1 hour ago, chiltonstar said:

Therapy, or buying another scope can cure this addiction.😼

Chris

I found both in the 80mm F15 refractor I just got for white light solar. It confirms why I love reflectors.

Regards Andrew 

[Stu]

4 minutes ago, andrew s said:

I found both in the 80mm F15 refractor I just got for white light solar. It confirms why I love reflectors.

Regards Andrew 

Not for solar surely? It is a shame the 80mm f15 doesn’t have a shorter OTA though I must say.

[johninderby]

Andrew did ask me for the details of how I shortened the 80mm f/15. 😁😁😁

[jetstream]

I wonder how many reflector owners push their scopes to the limit?

Under my best conditions the 15" Astrosystems/Ostahowski mirrors goes over 60x/inch on the moon. This is truly something to see, giving a wow moment every time conditions allow.

If people think 90x/inch in a refractor is amazing, try looking through a large dob capable of high power!

 

[Geoff Barnes]

You're right there Gerry!

I recently used my Vixen SLV 2.5mm to view the moon in the 12 inch Dob giving 600x and I was ready to put my feet down on the lunar surface, just mind boggling! 😀

[niallk]

I maxed out at 560x with my 6E 2x PM'ed on Jupiter in my 15" one exceptional night... amazing to see the image hold up.  That wasn't even pushing 40x/inch.  Maybe I should have left the Paracorr in for a bit more!! 😁

Drift time was getting fast though tbh, even with the scope's smoothness.  I'd feel the need to use an eq platform at this mag.

The atmosphere & cooling have such an enormous impact... A decent good night is 330x for me on planets / lunar.

[Stu]

56 minutes ago, jetstream said:

I wonder how many reflector owners push their scopes to the limit?

Under my best conditions the 15" Astrosystems/Ostahowski mirrors goes over 60x/inch on the moon. This is truly something to see, giving a wow moment every time conditions allow.

If people think 90x/inch in a refractor is amazing, try looking through a large dob capable of high power!

 

I reckon we would love to Gerry, it’s just with all the muck coming across the Atlantic our seeing just doesn’t support these big dobs at high power a lot of the time. I’m sure that’s why there are different preferences over there; they just work better at higher powers than they do over here.

[niallk]

... on the upside, I'm not tempted to purchase any Ethos SX EP's 😂

[John]

1 hour ago, niallk said:

... on the upside, I'm not tempted to purchase any Ethos SX EP's 😂

Been there, done that, decided that XW's were a touch better so eventually I let the Ethos SX's go.

 

[John]

2 hours ago, jetstream said:

I wonder how many reflector owners push their scopes to the limit?

Under my best conditions the 15" Astrosystems/Ostahowski mirrors goes over 60x/inch on the moon. This is truly something to see, giving a wow moment every time conditions allow.

If people think 90x/inch in a refractor is amazing, try looking through a large dob capable of high power!

 

As Stu says, the conditions over here usually preclude being able to really push a larger aperture scope. I have had a few nights over the past few years when I've been able to usefully use 400x - 500x with my 12 inch dob but most often that does not deliver any benefits.

With the refractors though, I reckon around 1 in 3 nights ands sometimes better than that, they can be pushed beyond 50x per inch with good results.

 

 

[Mr Spock]

A long time ago, when Saturn was high in the sky, a night of perfect seeing gave me my best ever view.  I was using an OMC-140, the early 'burgundy' type with 1/8th wave optics, and a Meade 6.4mm Plössl - x313. Saturn was crisp with an inky blackness to the background. Enke's division was easily seen.

Despite having several scopes nearly twice the size, I've never had a view like that since.

[Stu]

10 minutes ago, Mr Spock said:

A long time ago, when Saturn was high in the sky, a night of perfect seeing gave me my best ever view.  I was using an OMC-140, the early 'burgundy' type with 1/8th wave optics, and a Meade 6.4mm Plössl - x313. Saturn was crisp with an inky blackness to the background. Enke's division was easily seen.

Despite having several scopes nearly twice the size, I've never had a view like that since.

Likewise for me at x400 in an OMC200! Not since!

[Stu]

5 hours ago, Stu said:

Not for solar surely? It is a shame the 80mm f15 doesn’t have a shorter OTA though I must say.

Why confused @andrew s? Newtonians have many benefits, but I reckon it is fairly clear cut that a good refractor/Herschel Wedge will outperform a newt/solar film Combo.

[John]

My best Saturn was actually with an old C8 SCT that I used to own. Saturn was very high in the sky and the view with an 8mm TV plossl was absolutely breathtaking. No shimmer and no "coming and going" patches of best detail, just solid "Voyager views" for a couple of hours. Amazing.

I've had some really nice views since, particularly with the 12 inch dob but the really top drawer nights are thin on the ground.

 

[andrew s]

16 minutes ago, Stu said:

Why confused @andrew s? Newtonians have many benefits, but I reckon it is fairly clear cut that a good refractor/Herschel Wedge will outperform a newt/solar film Combo.

But that is why I was confused.  I got a refractror for solar and you said " not for solar surely "

Maybe you were being ironic.

Regards Andrew 

[Stu]

22 minutes ago, andrew s said:

But that is why I was confused.  I got a refractror for solar and you said " not for solar surely "

Maybe you were being ironic.

Regards Andrew 

It was the ‘it confirms why I like reflectors’ comment afterwards which seemed to imply you weren’t impressed with it?

Just crossed wires I assume? 👍👍