202 replies to this topic

[JerryWise]

Gosh-ah-rooty... Astrophotography is target dependent.

Everybody is right on choices here. The FSQ-106-ED is excellent for widefield but on the Arp objects you better have a long FL 14" or better instrument. Even the TOA-150 imaging the Sombrero gives gobs of detail away to a 14" LX200R. Scopes are like telephoto lenses on cameras. You snap on the lens that will see the object and fill the field with the desired frame. One size/style will never do everything in this hobby.

[Ziggy943]

A 6" deluxe F10 or F12 Mak should be competitive with a 4" APO. An 8" F15 Mak top quality mak (Intes Deluxe, TEC, etc) with a CO of 25% should compete well with a 6" APO assuming it has a good active cooling system.

A 4" APO can do a nice work as finderscope for any 6in, 7in or 8in specialized Maksutov but per sure the 8" resolution will kill the 6in APO resolution...

Maybe where you live this is true. As I stated above I sold my 8" F/15.5 because in my location it just didn't settle down 98% of the time.

Still, if the choice is strictly on raw performance a 6" APO will outperform a 6" MAK of any design.

If it's an economic decision the performance per dollar favors the MAK.

Throw in the 8" MAK vs 6" APO, for me, in my location the 160 APO is the better choice 98% of the time. I am more than willing to give up that extra performance 2% of the time. IMHO, the 160 outperforms or does no worse that the 8" MAK 98% (SWAG) of the time. At least by some high percentage.

The 8" MAK needs to be completely thermally stable to outperform a 6" APO. Outresolving a 6" class APO is strictly subject to the operating condition of the MAK. Stable... YES, Not stable ... not a chance.

In Florida of Mexico City YMMV.

[revans]

The FSQ 106 is for wide field deep sky photography... and at this it is one of the best scopes that money can buy... but it is certainly not designed for for hi res imaging of the moon and planets. I've taken quite a few deep sky photos with one. I personally really love the FSQ 106... but I love it for its intended purpose. It is not going to win any awards imaging Jupiter at F36 however...


Rick

[ColoHank]

Could someone explain to me why a larger Mak, in particular, is more likely to have cooling issues than either an SCT or refractor? Is it the mass of the mirror, a boundary-layer phenomenon, the extra thickness of the corrector, surface area vs internal volume or something else? All of the above, maybe? It seems to me a Schmidt is enough similar to a Mak (excluding corrector thickness) that the two designs would have about the same cooling characteristics. Even ignoring the thermal mass of a triplet-lens objective, why wouldn't the tube of a long refractor with all of its baffles be a reservoir and conduit for all manner of vexing internal air currents?

[revans]

I'm not sure... but looking at my scopes, the ones that cool down the best are the ones that have either vents in the back of the primary mirror that can be opened, or that have a removeable cover over the back of the mirror. Many people seem to install little muffin fans if neither of these provisions is present. I'm told that the scope with the absolute worst cooldown time is in fact a Mak... it is supposedly the rarely encountered 12 inch Questar that is no longer in production (but then, I've never used one).

Rick

Rick

[stanislas-jean]

Hi to all.
Frankly when comparing the 6" kinds they can show the same amount of details but not with the same contrast level especially when the contrasts to be seen are low to very low.
Apo or mct or sct or rc it doesn't matter in first. What is requested this is in first the roughness of the optics and the P/V front assessed globally.
Apo, we meet so many just diffraction limited and colorless,
sct, we meet somany just diffraction limited,
mct, we can meet so many with diffraction limited and some with acurate optics that are assuming the françon criteria eg p/v 8 front,
rc, we meet excellent to average scopes also.
I imagine when the word apo is given here this is the perfection (so more than p/v 8)that is mentionned and kept in mind.
When we speak about mct of small obstruction ratio, I think also p/v 8 and more. Indeed the obstruction is a handicap that can be quantified (see the theory CO31% means the equivalence of spherical aberration of p/v 4 so a strehl equivalent to 80% global on the scope). An apo of p/v 8 means a strehl of 95%.
On details of strong contrasts the ratio of contrasts seen in the apo and the mct is almost just the ratio.
On details of low contrasts near the limit of resolution this is almost the same ability to catch details. For medium contrasts the apo is the winner and bigger contrast are seen by a gain of say 30% max more than the level seen in the mct.
Now these expectations are well OK with no seeing. When the seeing becomes sensitive the apo is a great help showing bigger contrast than the mct.
Now considering a mak newton with 15% central obstruction the difference becomes so delicate that is very difficult to see a lost or a gain. The gain of the apo in that comparison shows almost no consistent gain for justifying the apo investment.
The conclusion may be to catch a mak newton of 15% CO with p/v 8 front mini in quality level with the star diameter at the focus plan well guarantied.
The mars sketch was performed with the M615 intes and with the last done with the 250mm newton of 25% CO. I doubt that an apo can do a consistent more job than the 250mm (that meet the françon criteria globally, not only on the primary), but could perform just a little more than the M615.
Here levels of scopes caracterised, observations and comparison between scopes make these conclusions.
6" is a good aperture for mars even now but that remains a 6" for any scope.
Stanislas

[SteveC]

Could someone explain to me why a larger Mak, in particular, is more likely to have cooling issues than either an SCT or refractor? Is it the mass of the mirror, a boundary-layer phenomenon, the extra thickness of the corrector, surface area vs internal volume or something else? All of the above, maybe? It seems to me a Schmidt is enough similar to a Mak (excluding corrector thickness) that the two designs would have about the same cooling characteristics. Even ignoring the thermal mass of a triplet-lens objective, why wouldn't the tube of a long refractor with all of its baffles be a reservoir and conduit for all manner of vexing internal air currents?

One thing I can say with authority is that the Intes Micro Mak OTAs are built like a tank. There's a lot of steel there. There were times, before I bought my TEC140, that I considered drilling several 1/2" to 1" holes in the OTA. I don't believe I'd sacrifice anything structually. Obviously I'm a wimp and I never acted on the impulse. The older I get, the more chances I seem to take, so someday you might be reading about my successful Mak surgery, or a request for information on purchasing a new OTA.

[JerryWise]

...
Now considering a mak newton with 15% central obstruction the difference becomes so delicate that is very difficult to see a lost or a gain. The gain of the apo in that comparison shows almost no consistent gain for justifying the apo investment.
The conclusion may be to catch a mak newton of 15% CO with p/v 8 front mini in quality level with the star diameter at the focus plan well guarantied....

Stanislas, I know little about Mak Newts so forgive my asking. Where can you get one commercially with a 15% CO and P/V 8? Thanks.

[isramirez]

... Where can you get one commercially with a 15% CO and P/V 8? ...

Jerry, sorry but I can not believe it ... Intes Micro MN68 is the scope... i said that in my first post in this thread!

[maknewtnut]

A lot of great points, but almost just as many subjective opinions stated as fact.

For example, I owned a 250mm D-K and ran it side by side with a 140mm apo(granted, not 6", but close enough to make the point). The larger scope could not perform to it's capablities anywhere near a point one could refer to as consistent. I did not engage in planetary imaging, so the smaller refractor won hands down. As stated, imaging is object specific.

As for several comparision that tended to infer a 2" difference in comparitive image quality, why not go 1", which is far closer to a realistic comparison. For example, a high quality 7" Newt or MakNewt will go toe to toe with a 6" apo, with the only noteable difference being the refractor has the edge in widefield imaging capablity(primarily due to illuminated field size).

Other comparisons that involved a 2" difference in aperture, and yet favor the consdierably smaller refractor, are most certainly opinion only. Given the number of opinions based on the same comparison that favor the larger Mak, this is certainly not set in stone. Considering differences in aperture as it relates to gains in resolution and light gathering are more pronounced as aperture decreases, one could easily tend to place more weight in those that favor the 6" Mak. Having performed an extensive 4 part review making exactly the comparison(comparing a TV101 to an MN66 on AM forums years ago), I sure as heck favor the latter as well.

As for one of the latest examples referred to, the f/8 MakNewt, the strengths of the design type are greatly diminished once one goes slower than f/6. A Newtonian of comparable aperture and focal ratio with great optics and tube design offer more pros with fewer cons at this speed.

[JerryWise]

... Where can you get one commercially with a 15% CO and P/V 8? ...

Jerry, sorry but I can not believe it ... Intes Micro MN68 is the scope... i said that in my first post in this thread!

Here is your first post:

I believe a premium 6"APO from AP, Taka or APM is a lot for a 6"MakCass but per sure a 6"MNF6 or 6"MNF8 will do a fantastic match!

I didn't get too much out of your first post as far as what I was asking ("Where can you get one commercially"). Thank you for providing a link in your response along with the entertaining subtleties.

[JerryWise]

Mark, is this the scope Isramirez is talking about. It looks good and very interesting especially with the FT focuser. Is the general impression this will compete one on one with a Tak TOA-150?

[darylf96]

I think such a choice is very simple: If you have the bucks to buy a good 6 inch Apo, you are both lucky and have an excess of disposable income. If money is a factor, buy the Orion 190mm MN, which is very versatile, good for both imaging and observing, and your savings can be used toward
a good mount.

Daryl

[ahlberto]

The best planetary scope ive looked at the time was a Skywatcher mak cass 180mm after 5 hours of cooling.Jupiter was so photto like...it let my C8 on the dust as all the 12" and 18" reflectors at the star party.Its one of the most amazing planetary scope ive seen and is beenn selling cheap at 500 pounds in england

[ahlberto]

And i bet the skywatcher 180mm mak cass will outperform easily any intes of equal aperture.You will be surprised how easily this mak cass beat an expesive intes.

[revans]

You know... sometimes a "fact" is just the majority of a collection of subjective opinions....

Anyway... I don't change my mind... if you think 6 inches is superior to 10 inches... then that is your priviledge as a rugged individualist.... not for me though )) I spend my money better than that



Rick

[Fomalhaut]

And i bet the skywatcher 180mm mak cass will outperform easily any intes of equal aperture.You will be surprised how easily this mak cass beat an expesive intes.

=> Why should it?? The Intes-Micro Mak-Casses are widely agreed to be essentially perfect.
(Of course the Skywatchers come from China and hence are cheaper, if you like this...)

Chris

[ahlberto]

They are not perferct,and in this test http://www.cieletesp..._Alter_M603.pdf theres the proof.The star test shows a grave error in optics that should be detected since they are"and made and perfect".And ive have saw another bad optics wich a star test easely shows...But they are indeed great scopes but they are not perfect and tey arent better than a skywatcher.

[JerryWise]

Mark, is this the scope Isramirez is talking about. It looks good and very interesting especially with the FT focuser. Is the general impression this will compete one on one with a Tak TOA-150?

I was thinking of buying a MN68 since my MK66 isn't living up to what I expected. If the MN68 or any other much cheaper scope can perform like a TOA-150 it is foolish keeping APO money tied up in one. The MN68 seems similar to the OTA linked above but I searched Astromart for recent sales. This ad is very informative. If you don't have an Astromart account the seller is explaining why he is selling his almost new MN68 "I would have to say that the scope's performance is not quite what I expected--5" apo views. " I agree with the seller and all here saying they are excellent scopes. Not APO excellent but a good value. Think I'll stick with APO for wide field imaging/visual and SCT/Newts for big bore hunting. Its a good discussion though. Thanks Larry for bringing it up.

[SteveC]

The best planetary scope ive looked at the time was a Skywatcher mak cass 180mm after 5 hours of cooling.Jupiter was so photto like...it let my C8 on the dust as all the 12" and 18" reflectors at the star party.Its one of the most amazing planetary scope ive seen and is beenn selling cheap at 500 pounds in england

I guess the laws of physics ceased to exist for a short period of time over this star party.

[isramirez]

And i bet the skywatcher 180mm mak cass will outperform easily any intes of equal aperture.You will be surprised how easily this mak cass beat an expesive intes.

Sorry ahlberto but we also have access to skywatcher and many other scopes in America and we know what we are talking about...

[isramirez]

If you don't have an Astromart account the seller is explaining why he is selling his almost new MN68 "I would have to say that the scope's performance is not quite what I expected--5" apo views. " ...

I tend to believe the people is a bit sick because the word APO and because the big amount of money they paid for one of those scopes... in the solar system astroimaging forum there are tons of guys with 4in, 5in or 6in APO scopes and most of the time their images are just big losers so... how a magnificent!!!, incredible APO view!!! is just a bad picture when compared to the pictures coming from other scopes in similar conditions? ...easy answer

Amateurs with APO scopes can see more with their scopes but because their imagination or fantasies at the eyepiece but the laws of physics don't have that issue and that is why many APO lovers have the following excuse "I'm not good for astrophoto..." when they make public their pictures

[JerryWise]

Isramirez, nobody can argue with that logic. :bangbangbang:

[isramirez]

Jerry,

What i'm trying to say is... per sure a 6in premium APO is a fantastic very well made telescope but at the end it is just a 6in telescope... as I remember there was a very famous professional astronomer that found "canalis" in mars with his very powerful refractor telescope many years ago... and now that we can see mars much better than ever in the past where are the "canalis"?

Easy answer, they were in the mind and fantasies of the astronomer at the eyepiece...

[JerryWise]

Agreed. I like the description "averted imagination".

There are things an APO can do well. Here is an image of the Horsehead area taken through my FS-78 ED doublet. This is a 3" refractor. I mentioned earlier I paid $900 for this scope and the camera is a $500 Canon. You can actually see the Alnitak double in the glare and the Horse Head can be made out. You don't have to work hard getting passable images with those scopes. They do their job well. I like my ETX but I doubt a 3" Mak is going to cover that area.

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