355 replies to this topic

[deSitter]

It's not a Gregory, but a Rumak. 

 

 

Clear skies!

Thomas, Denmark

Interesting, fixed 2ndary!

 

-drl

[JuergenB]

That one seems to be kind of a unicorn. I found a report which dates from 2013 here: https://www.photoinf...mm-Maksutov.htm.

 

Not sure whether these MK24020 are still produced. Aliexpress now shows a "404" with the above links.

 

Juergen

[Astrojensen]

 

Aliexpress now shows a "404" with the above links.

?? The links still work fine for me.

 

 

Clear skies!

Thomas, Denmark

[luxo II]

The page loaded for me.. yes Bosma was making them 10 years ago, no idea what they're like as I've never seen one here. At that price most locals would buy a C8 instead rather than an unknown quantity.

[maroubra_boy]

Well, well, well...

 

THAT is certainly new!

 

Would be interesting to see how good it is optically and if it shows mirror shift.

 

Specs say fully coated rather than multi coated.  The Vixen style dovetail might be a little lightweight as it is not a lightweight OTA at 11kg.

Edited by maroubra_boy, 23 February 2024 - 07:25 AM.

[deSitter]

That one seems to be kind of a unicorn. I found a report which dates from 2013 here: https://www.photoinf...mm-Maksutov.htm.

 

Not sure whether these MK24020 are still produced. Aliexpress now shows a "404" with the above links.

 

Juergen

Thomas points out that it's listed as a Rumak but is it? There is no adjustment so it could only be a small aluminized glass riser cemented to the meniscus. That would be difficult to manufacture reliably without a lot of handwork. But who knows?

 

-drl

[Ed D]

Here's a blast from the past:

 

Vintage 90mm Mak lens

 

It's a Celestron 90mm Mak f/11 1000mm that can be used as a camera lens, spotting scope, or telescope.  I mainly use it as a terrestrial/spotting scope and can be seen in the pictures with a 45* correct image diagonal.  I have no idea how old it is, but it is an oldie that gets used a lot.

 

I also have an iOptron 150mm Mak that I have owned for many years:

 

Old photo of iOptron 150mm Mak

 

It has given me fantastic planetary and lunar views and photo images.  I haven't used it much for several years due to commitments that chip away at my time, and injuries I sustained a few years ago that now make it somewhat difficult to handle.

 

I used to have a 127mm Celestron Mak:

 

Celestron 127mm Mak dwarfed by the 150mm behind it

 

I sold it years ago and still regret selling it to this day.  What I loved about that one was the compact size and light weight, and the really nice views and photo images.  Many times I wish I would have sold the 150mm and kept the 127mm.

 

[JuergenB]

Thomas points out that it's listed as a Rumak but is it? There is no adjustment so it could only be a small aluminized glass riser cemented to the meniscus. That would be difficult to manufacture reliably without a lot of handwork. But who knows?

 

-drl

As I haven't seen a Bosma 200 or 150 in person, I cannnot confirm the design, but iOptron claims that the iOptron/BOSMA 150/1800 is a Rumak, so the 200/2400 should be one as well.

 

Judging from the pictures, the secondary mirror support of the 150 looks similar to that of the 200/2400. You are right that the secondary is cemented and cannot be collimated. The collimation instructions for the 150/1800, https://www.ioptron....Collimation.pdf, only mention the adjustment of the primary. 

 

Juergen

[ABQJeff]

Hello, I have always wanted a 5 or 6 inch Mak Cassigrain, I currently own and I am very happy with my 6"SCT but I always wondered if a 5 or 6 inch Mak would out perform the SCT on and especially the moon. I have seen the moon in all sorts of scopes.  Had a 90mm Meade Mak many years ago that scope was awesome the contrast was so good!! I almost bought the ETX 125 but it was not on the market when was buying a scope so I bought the 6 inch SCT instead. 

A 150mm Mak vs a C6 will be practically indistinguishable on DSO, and on planets/Moon the Mak will have a little better contrast, but it would take better than average seeing to really see the difference.  Optically the Mak has a little larger corrected spot size.  So yes the Mak is better optical design BUT it may not noticeable in average conditions and both are mass produced instruments, so there is that variance.  Mak won't need as much collimation but is also heavier.  C6 will be able to get a little wider views and is a lttle more 'all purpose' instrument.  Buy a 150mm Mak  and see for yourself, most places allow for 30 day returns.  Or keep both for their unique strengths!

Edited by ABQJeff, 23 February 2024 - 04:51 PM.

[luxo II]

 The collimation instructions for the 150/1800, https://www.ioptron....Collimation.pdf, only mention the adjustment of the primary. 

Those prone to fiddling with the scope must be so disappointed

[Chuck2]

C90 Astro, most fun grab ‘n go:

https://www.cloudyni...9-b706ea5a7639/

https://www.cloudyni...8-fe3ef81509a4/

 

https://www.cloudyni...b-02750ad25e31/
 

[Terra Nova]

I’ve had an old orange Celestron C90, two Lomos (95mm and 70mm), a 100mm and 127mm Synta, and a 1987 Questar standard with broadband coatings. My favorite will always be the Questar! It was a fine scope, and now that I’ve moved to the condo, I wish I would have kept it. It was truly a fine instrument.

Well, I did it again! Here’s my current (and currently only) Mak. And it’s my new fav! It’s a 1969 Questar Standard with a Cervit primary and BroadBand-coated optics.

Attached Thumbnails

• 

[RAKing]

Everyone loves the Questar!  

 

I remember flying the old TWA Sunday morning flight from Washington Dulles to Los Angeles back in the 1970's.  Questar always had a big advertisement in their company flying magazine, and I spent half the flight daydreaming about the views I could get with it.  I was a frequent traveler back then and my Modis operandi was to buy an inexpensive refractor where I was stationed, use it during my posting, then give it away when I came home.

 

Enjoy!  

 

Ron

[ABQJeff]

Well, I did it again! Here’s my current (and currently only) Mak. And it’s my new fav! It’s a 1969 Questar Standard with a Cervit primary and BroadBand-coated optics.

Beautiful Mak, looks to be in great condition!

[Terra Nova]

Beautiful Mak, looks to be in great condition!

Thank you. It is in lovely condition.

[maroubra_boy]

Bosma makes an 8" f/12. I've seen it on Aliexpress. 

 

 

Clear skies!

Thomas, Denmark

I sent them a message asking about it.  It is no longer available.  It hasn't been made for a few years now.

[maroubra_boy]

That BOSMA 8" Mak has not been made for several years now.  They are being advertised on Aliexpress, but the retailers doing so have no stock and the ads are just clickbait.  I messaged the two retailers who are advertising this scope.

 

The Amazon UK site also advertises it, and with the jolly price of 11,000  British pounds, or nearly US$14,000.  One of the dodgiest ads I have ever seen too.

 

So, yeah, Maks larger than 7" are not being made.

[Magnus Ahrling]

Beutiful Q, Terra I have never looked trough one, not even seen one.

 

Magnus

[vahe]

That BOSMA 8" Mak has not been made for several years now.  They are being advertised on Aliexpress, but the retailers doing so have no stock and the ads are just clickbait.  I messaged the two retailers who are advertising this scope.

 

The Amazon UK site also advertises it, and with the jolly price of 11,000  British pounds, or nearly US$14,000.  One of the dodgiest ads I have ever seen too.

 

So, yeah, Maks larger than 7" are not being made.

Orion UK offers 8" F20 Mak (OMC200) at $8700.00.
.
Vahe

[maroubra_boy]

Is it in stock?

If it is new fabrication, who is making the meniscus correctors for them, because they have something no one else has.

Alas not a brand I would entertain the idea of buying from though. Certainly not sight unseen. The overwhelming number of horror stories about the instruments they offer & their attitude towards customer service when problems pop up, yeah, I would never consider taking on any gear of theirs unless I could test it until it bled. A real shame if they are still able to source such optics.

Edited by maroubra_boy, 26 February 2024 - 03:56 PM.

[alnitak22]

Well, I did it again! Here’s my current (and currently only) Mak. And it’s my new fav! It’s a 1969 Questar Standard with a Cervit primary and BroadBand-coated optics.

Pretty Questar…and pretty Pronto!

[Terra Nova]

Thank you Magnus and Alnitak

[RichA]

Where attention does need to be paid is the design and fabrication of the baffle tube on the primary mirror and the secondary's assembly.  THIS is where the vast majority of loss of contrast is happening.

 

Ever wonder why some Cassegrains have just outstanding contrast and others not?  They all have a central obstruction.  The size is of the obstruction is not the cause either as some have large obstructions too.  Very few of these scopes with outstanding contrast have a series of baffle rings running down the inside of the OTA as well.  But what they all have in common is how the baffle tube and secondary's assembly has been designed and made.  And what you won't find is black anodised aluminium nor shiny black plastic.  Not in a Mewlon, not in an Vixen VMC260L, not in an APM-Wirth Mak.  The Russian made Maks, such as from Intes and Santel also have very good contrast, but a little step down from these others.   A loooong way behind are mass production SCTs.

 

Below are two pics showing the insides of an SCT and an Intes Mak with as similar as possible angle of incidence of light and camera position to show the source of the difference in contrast between the two scopes.  The SCT has shiny black plastic and black anodised aluminium EVERYWHERE which at glancing angle of incidence, which is the way light falls on these surfaces, is what produces the internal reflections and scattered light that is the source of the reduced contrast.

 

Yes, the Intes has a series of baffle rings down the inside of the OTA, but these actually do very little.  My 9" Santel Mak has no such baffle rings and the quality of contrast is every bit as good as an Intes Mak.  It isn't quite as good a Luxo's 10" APM-Wirth Mak (all three scopes actually make use of the same Intes made glass!!!), and when I looked down into the OTA of both scopes (Santel and the APM-Wirth), the differences were small but made all the difference.  The Santel still had a couple of shiny spots and the design of the baffle tube was different which meant the contrast in my gorgeous Santel Mak is a little lower than Luxo's Mak, but it still stomps all over an SCT.

I had a 6 inch RC with a baffled tube.  It had poor contrast likely due to the 40% central obstruction.  Also, what sources of reflected light are you imagining? If you are looking at a star field, it's hardly floodlit.  The Moon, sure, but under what other circumstances are you going to encounter enough light for any scatter to matter?

[maroubra_boy]

If you have a 40% obstruction, then you may want to reconsider an RC for visual use.  They are intended for AP, not so much for visual.

 

Have you compared it to a known Cassegrain of outstanding contrast?  I have not discussed whatever RC you are using (you don't mention the brand) as I will only discuss what I have experience with.  Then if contrast is reduced, wouldn't you want to look for ways to improve it, which includes the quality of blackening of the baffle tube and the secondary's assembly - again something you did not mention, only the size of the central obstruction like it is the only factor in reduced contrast.  You also offer nothing about why there are some Cassegrains with far better contrast than others, yet the % difference in central obstruction can be insignificant between these.

 

Other circumstances?  Well, you tell me.  Looking through the many different types of Cassegrains as I have side by side, there are blatant differences in contrast, not just with the Moon.  The Moon is the easiest one with which to identify the source of internal reflections and scatter, something you are not realising.  How else would you explain the differences in contrast between an SCT to an Intes Mak to a Mewlon?  The difference in % of central obstruction is not a factor.  But there is a difference in contrast.  The amount of scatter and reflection that a poorly designed and manufactured baffle tube and secondary housing impacts in all situations, not just the Moon.  Comparing scopes side by side while looking at the exact same object will show these differences.  Can be subtle the differences, but they are there and this is a discussion on what impacts on contrast.

 

Another source of contrast lose is poorly polished mirrors.  This can be a HUGE factor and again one I have seen with brand new Newts of different brands with the same technical specs and construction.

 

There are also environmental factors that impact on contrast, but this requires the observer to be able to identify good conditions vs mediocre and why it is important to be able to do side by side comparisons so different scopes are compared under the same conditions.

[archer1960]

I had a 6 inch RC with a baffled tube.  It had poor contrast likely due to the 40% central obstruction.  Also, what sources of reflected light are you imagining? If you are looking at a star field, it's hardly floodlit.  The Moon, sure, but under what other circumstances are you going to encounter enough light for any scatter to matter?

All it takes is a bright star. Vega, Alnitak, and many others are plenty bright to get ghosts and reflections.