which planet killer?

[Stu]

1 hour ago, Stub Mandrel said:

I thought the man said Maks have along cool-down period

Pete obviously put it in the freezer to speed things up  

[Alan White]

19 hours ago, Moonshane said:

Probably the case to be honest. I have done what Paul suggests though and bought a range of scopes! Doesn't stop me hankering after a 100mm Tak though!

 

Don't most of us Shane, however hanker for and have a two very different things.

[Alan White]

6 hours ago, mikeDnight said:

To them I'm just an eccentric nut who sits out at night in 6" of snow, and in subzero temperatures with tears in my eyes because of the cold breeze, to draw detail visible on a tiny planetary disc. Surely only a like-minded nut would be interested in a portfolio? 

Oh Mike that made me laugh.
Have to say many of our families and friends must think the same of many of us, my lot do.

[Alan White]

8 hours ago, Peter Drew said:

I've said it before, if the seeing isn't good enough to use a decent size telescope, i do something else.     

Like go to Tenerife to get the seeing Peter 

I must try and get that one to fly with 'The Finance Officer',
if you don't hear from me again you know what happened!
 

[Alien 13]

Floaters would rule out any frac for me, Maks are ok though.

Alan

[paulastro]

7 hours ago, mikeDnight said:

If I pop my clogs you can have my sketch books Paul, as I doubt my wife or sons will place much value on them. To them I'm just an eccentric nut who sits out at night in 6" of snow, and in subzero temperatures with tears in my eyes because of the cold breeze, to draw detail visible on a tiny planetary disc. Surely only a like-minded nut would be interested in a portfolio? 

I'd rather your book comes out while you've still got your clogs on .  Mind you, if the worse comes to the worse, I'll keep looking in the skip outside your home in case your drawings are thrown out!

[Alien_Photons]

If you have the mount the refractor. If you don't have the space the mak. If you don't have the time the refractor......

What do you want to see as these will all show the same image differently. I tried them all of different sizes to those you mention but it's all true what people say about them.

None of them are planet killers. They all have compromises. The question comes back to what you are prepared to live with physically and optically.

You may need to try all three to work it out for yourself. It's the only way to be sure.

[jetstream]

On 9/4/2017 at 15:48, catburglar said:

but the moon is still here, and there's lots to see.

Your 7" should be Vg for lunar detail but if seeing co-operates the larger the aperture the better assuming equivalent (or better) optics. The difference between my 10" dob and 15" dob for lunar is staggering... the additional fine detail brought with the aperture increase is well worth it. My 15" runs 20% CO which is a contrast friendly figure.

If I were to add a scope for additional detail on the moon and planets and already had a 7" scope, it would be a VX12L like Johns scope. They run a 21% CO, which is VG for contrast transfer IMHO.

 

[Dave1]

Really you need to provide us with the F ratio numbers. Your also not comparing apples to apple. When it comes to telescope aperture and central obstructions. You should compare clear aperture for clear aperture. I've seen a ray trace for the Skywatcher Skymax 180 pro. Its actually 170mm. The central obstruction on the 180 pro is 24%. So 170 - 24% = 129.2. But the F ratio is also critical the higher the F ratio the narrower the view, but the bigger the image will appear. So an 130mm refractor at F8 will have a smaller image of a planet compare to a 130mm refractor of F15. 

Apochromat refractors will bring the red, blue, and green light waves to the same plane, an achromat does not. However refractors have better low frequency detail compared to a telescope with a central obstruction. Which means you will see more of the very dim detail on offer. A telescope with a central obstruction will have better high frequency detail. The Mak will have slightly lower contrast. 

A good page on this is http://www.brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/forum/c-o's.html

Having said that I've just ordered the latest 180 Skymax Pro. Which apparently has green paint? According to the importer OVL.

[Stu]

3 minutes ago, Dave1 said:

But the F ratio is also critical the higher the F ratio the narrower the view, but the bigger the image will appear. So an 130mm refractor at F8 will have a smaller image of a planet compare to a 130mm refractor of F15. 

That's only strictly true if you are talking about using the same f/l eyepiece. You would need to use eyepieces of roughly half the focal length to get the same image scale but a 130mm f8 refractor has a focal length of 1040mm so you can get to x250 quite easily with a 4mm eyepiece.

[Dave1]

Yes well pointed out, that's if you use the same eyepiece in both telescopes. And 250 X is only going to be able to be used on nights of good seeing. 

[Peter Drew]

The characteristics of the 180 Mak aren't quite as bad as it seems at a first glance. The reduction to 170mm effective aperture is probably due to the telescope not having an oversize primary mirror. The lightpath from the corrector diverges slightly so if the mirror is the same size as the corrector the outer rays will miss the primary. The telescope will still have the resolution of the aperture and the reduction in light gathering will be the subtraction of the area of the obstruction which is quite a small percentage. 

[Rainmaker]

On 9/5/2017 at 05:15, catburglar said:

Any thoughts regarding 3 scope options for lunar/planetary observing- specifically visibility of low contrast details. 

7 inch Mak, 6 inch F/8 achromat or 5 inch ED doublet

Cooldown and mounting issues aside, does the obstructed aperture of the larger Mak beat the others, or does the smaller ED have the edge in contrast that trumps the larger aperture scopes. The 6 inch F/8 is in there just because they regularly crop up and I've never tried one.

I would think the 7" Maksutov would be the best option of those three for a 'planet killer' if you have reasonable seeing conditions and the patience to allow the Mak an hour to cool to ambient.

 

 

 

[L8-Nite]

In one word, Q7. In five words, Q7 and relocate to Chile.

[Dave1]

3 hours ago, Rainmaker said:

I would think the 7" Maksutov would be the best option of those three for a 'planet killer' if you have reasonable seeing conditions and the patience to allow the Mak an hour to cool to ambient.

 

 

 

Could also keep a Mak in an unheated out building. Much closer to outdoor temps requiring little to no cool down time. That's what I will be going with mine.

[catburglar]

Thanks to all for the replies- this was primarily an hypothetical question...my Mak is a Meade F15 LX50 - an oldie but goodie as far as I can see. But, I've never compared it to a largish unobstructed refractor- so that was the nub of the question.

I am now thinking of designing  a folded refractor F12 or F15 with a lens from Istar or similar- shouldn't be so difficult to mount if I get the tube length down to a meter or so, and then I might be able to do a side by side comparison.

[Rainmaker]

13 hours ago, catburglar said:

Thanks to all for the replies- this was primarily an hypothetical question...my Mak is a Meade F15 LX50 - an oldie but goodie as far as I can see. But, I've never compared it to a largish unobstructed refractor- so that was the nub of the question.

I am now thinking of designing  a folded refractor F12 or F15 with a lens from Istar or similar- shouldn't be so difficult to mount if I get the tube length down to a meter or so, and then I might be able to do a side by side comparison.

Interesting idea, I previously had an Istar 150mm F10 which was a very nice scope ....  I now have a TEC 8" Mak Cass and having used a TOA150 and a TOA130 extensively, I think it would take a 7" Apo refractor to match the views of the 8" TEC Mak.  I use mine with Zeiss binoviewers and Takahashi LE and Abbe eyepieces.

 

[Alkaid]

I heard that the humble 200P dob was a bit of a planet killer on a budget.....and you could ring the OTA and stick it on an EQ mount for the tracking if you fancied....I am toying with this idea at present.

[catburglar]

I know that a large NEWT is the sensible answer- Moonshane pointed that out much earlier in the thread.

However, that did get me thinking about something a little more unusual. I might fancy a Schiefspiegler- reflecting so no CA, unobstructed so no contrast loss,  and they look cool!

 

Seen a small ome in the DIY forum here, so doing a bit of googling now.

[Alkaid]

1 hour ago, catburglar said:

 

I might fancy a Schiefspiegler

 

A what? 

Forgive me, I have been away from the forum during the summer months, hadn't heard of one of those....what is it?   (Intrigued!)

[catburglar]

The name refers to a range of unobstructed reflecting telescopes that use mirrors tilted at shallow angles to the optical axis....ere's a link to a build thread for a v dainty one; https://stargazerslounge.com/topic/293244-kutter-2-f282-finished/?tab=comments#comment-3211756 and below are a couple of links a slightly larger ones http://spider.seds.org/scopes/pd2.jpg and finally one that might be a bit easier to construct https://stellafane.org/convention/2007/images/scopes/Entry19/P8112729.JPG

 

they tend to be relatively small aperture and long F/L, so never going to fit in the pleides in one fov, but that's sort of the point......

 

[tony210]

Hi - don't think anyone has mentioned the Tak  Mewlon 210- good aperture and low central obstruction so good contrasty views - have got good views of Saturn Jupiter and Mars and great images.

[John]

All my scopes are planet killers if the seeing is nice and stable

 

[Paz]

This has been an interesting thread to read. I've never yet looked though a high end refractor although i hope to get one at some point in the future.

For now the best planetary views I've had have been with the VX14. Often I will stop it down to an unobstructed 137mm when at lower magnifications or in worse conditions.

My maksutov is next best - images are not as detailed but are super clean. I like this so much I'm looking to change from a 127mm mak to a 180mm. The only problem is... nobody wants to sell theirs!

[F15Rules]

On 05/09/2017 at 10:33, Peter Drew said:

I've said it before, if the seeing isn't good enough to use a decent size telescope, i do something else.     

Well, Peter, in that case you must spend a lot of time doing something else! ??

Seriously though, smaller, lighter scopes have a lot going for them in UK skies. They are also much easier to set up and use for short sessions, and I for one prefer regular shorter sessions to infrequent all nighters.

Getting back to the original posting, I'd have to agree that a good 7" Mak will outperform any high end doublet if cooled well and in good conditions.

My best ever lunar views were with a Ylena (Lomo) 6" 14 Mak, and later with an Intes MK67 (also a 6", but F12 as I recall) not far behind. The contrast and sharpness were superb.

The other great thing about Maks is that you view through them in the same orientation as a frac, which I much prefer.

Nowadays though, I have an FS128 and Vixen ED103s (both doublets, the Tak Fluorite and the Vixen FPL53), and they tick all my boxes namely: best in class image sharpness and contrast on more nights, fast cool down, ease of use, versatility and sheer beauty to look at. I won't be changing any time soon??.

Dave