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Old 01-03-2020, 09:46 PM
ecsaow (Evan)
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Achromat vs Mak

Currently have a SW 4" f/10 achromat and have been looking at possible upgrading to a SW 127 mak.

Wondering whether it would be an upgrade of sorts, with a little more aperture and more ergonomic and compact for transport.

Basically my question is, would a 5 "Mak be an improvement on an 4 " Achromat of similar aperture ?
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Old 01-03-2020, 10:17 PM
raymo
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Well, you will get rid of the CA around bright objects with the Mak, which is a positive. Everything will be a bit brighter, but not a lot. The Mak is nice and sharp. The Mak having a much longer focal length is a great planetary and lunar scope, for visual and astrophotography, but having said that, it is very slow photographically, and not a good choice for imaging of deep sky objects such as nebulae.
Pros
planetary and lunar inc imaging.
Nice and sharp.
Compact size.
More aperture.
No CA

Cons
Takes longer to cool down to the ambient temperature.[ Being small, not too long].
Photographically very slow for deep sky work.
Narrower field of view.

Your choice, no one scope is great at everything, they are all compromises.
raymo
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Old 02-03-2020, 12:00 AM
Ukastronomer (Jeremy)
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My advice is it is not worth it, especially with the low small aperture, it is again a low cost scope, beginners, birding etc, sorry, ok as a grab and go.

Me, pre owned or new 6" reflecting scope/DOB

Is an 1100cc car better than a 1,000 cc car ?
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Old 02-03-2020, 12:09 AM
ecsaow (Evan)
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Hey Raymo, thanks for your thoughts
I'm not to bothered at the moment with getting into to AP.
I'm mainly using my little setup in a light polluted urban area, and so for me Moon, planets and some additional extras will suffice.

The cooling down aspect of the scope is not that problematic for me, I simply pop my scope out on the balcony, an hour or so before.

My line of thinking was that a MAK might give me a more APO like experience without the price tag for similar aperture Apo

And like you say, its all about compromises, but you've helped me confirm my thoughts about it, as I ordered one yesterday, so should be arriving this week. Will set the 2 up side by side and see if the reality matches. Of course as soon as it arrives the I expect the skies will be terrible, so will probably sit there looking at the thing for a week or so before I can test it out.

Appreciate the pros & cons,

Cheers Evan
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Old 02-03-2020, 12:13 AM
raymo
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Jeremy, he wants a scope that is compact for transporting, something a 6"
Newt is not, and I have to disagree, the 127Maks are usually optically very
good, most definitely not just a birding scope. The 127, 150, and 180 are
all da---d good value for money. They are not a great all purpose scope, but what they do they do well.
raymo
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Old 02-03-2020, 12:19 AM
raymo
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Looking forward to seeing your critique Evan.
raymo
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Old 02-03-2020, 01:23 AM
ecsaow (Evan)
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Hey Jeremy
I hear you, and agree, its still a low cost scope and a beginners, and your right in that a reflector with larger aperture maybe 6"/8"would probably be the same price.

I need something that I'm going to use continuously and that is ergonomic in size.

Even my 4"inch achro is sometimes a pain with some of the viewing positions you can end up in.

I know I'm whinging, but I find myself using my SW Startravel f/5 120 moreso than the f/10 achro, even though its more for wide FOV.

I have figured that "5-6" of any type of scope would be my limit for portability and practicality of use. I use a SW Stardiscovery mount,manually, without the GOTO the batteries are out, so its just a light simple mount.

Would rather be out there with something small and compact that I can pick up with one hand. For me, the bigger, the more awkward, and in the end the less use.
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Old 02-03-2020, 06:31 AM
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mental4astro (Alexander)
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Hello Evan,

While the aperture gain in the 127 Mak isn't all that much, yes it will be a significant improvement in optical quality over the 4" achro. It will allow you to go to 250X without showing chromatic aberration as Raymo says.

As for the cooling, DON'T let it cool down!

The whole problem for Maks & SCTs in cooling is the heat plume that develops because of the warm primary mirror & baffle and the cold metal tube. So, if the tube is not allowed to cool, say by wrapping it in an insulating wrap, the temp differential between tube and primary mirror & baffle won't occur, and hence no heat plume. And you can rip the max magnification from the Mak from the very start of your viewing session.

I've been doing this for several years now, first with my orange tube SCT, through to the 7" Intes Mak I had and now with the 9" Santel Mak I use. No cooling down time, but straight to work.

For the Maks I made the insulating wrap-come-dewshield out of white Coreflute. Where it extends over the corrector I lined the inside of the wrap with black contact felt. The colour of the wrap is vitally important!!! DO NOT USE A BLACK OR DARK MATERIAL! Black cools down to below the ambient temperature and as a result will both act to accelerate the cooling of the tube ( ie induce the heat plume we want to avoid) plus it will attract dew a whole lot faster than white or a silvered surface.

The Coreflute wrap is made by cutting down every second cell on the outside surface. This allows the wrap to easily roll on itself and around the tube. How far out from the corrector you make the dewshield part, the minimum I would suggest is the aperture of the scope. This wrap will also extend the time the corrector stays dew free compared to just having a dewshield that only extends out from the corrector. It won't totally prevent dew, but will markedly extend how long the scope goes without dew forming. I also cut the necessary slots and holes to accommodate the handle, finder scope shoes and anchor points for the dovetail plate so the whole of the scope is wrapped.

Some people have also used a type of aluminized building insulation that is on a rubber mat/sheet. It doesn't need to look pretty. It just needs to work.

Alex.
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Old 02-03-2020, 11:45 AM
ecsaow (Evan)
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Hey Alexander
This is interesting stuff, so your wrapping the whole scope basically with this Coreflute plastic type material. Dark felt lining the inside and white on the outside. I think if I'm not mistaken that Coreflute is the type of material they use to make signs normally, that are lightweight eg, the "for sale, for lease" signs ?

Are you using a stanley knife to score every second cell or so to enable it to fold, is that the method you've used ?

Will definitely look into this

Cheers Evan
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Old 02-03-2020, 12:24 PM
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mental4astro (Alexander)
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Yes on both the signs and Stanley knife

You may be lucky enough to find an old Coreflute political poster that will be large enough to do a small Mak. Failing that Bunnings has the stuff. It's not expensive, and it will last you many, many years as it is water proof!
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Old 02-03-2020, 01:49 PM
ecsaow (Evan)
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Stunning sketches there on your Blog Alexander, really impressive !
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Old 02-03-2020, 04:16 PM
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mental4astro (Alexander)
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Thanks Evan

I nearly forgot, another material that can be successfully used as a wrap/dewshield is a light coloured foam yoga/camping mat. These are cheap and easy to cut as needed. I used one of these with my C8 - I found the mat during a council big rubbish chuck out I painted the dewshield end of it with black paint. Served me well for many years. I couldn't extend the wrap further down the tube because of the forks, but it still performed really well without needing a cooling period.

Alex.
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Old 02-03-2020, 06:24 PM
N1 (Mirko)
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Good thread. Refractors are great but going from a 4" achromat to a 5" Maksutiv absolutely will result in an improvement on the items that matter to the OP. And if the mak is too slow, there is always the C5.

Must look into insulating my own SCT Alex style. This will also help deal with drew in the field methinks.
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Old 02-03-2020, 11:06 PM
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I can attest to the virtue of insulating vs cooling down of a Mak/SCT also...

I will gratefully acknowledge both Alex & Wavytone for introducing me to this.

I was skeptical at first, particularly since I live in FNQ where the temps are very warm & the air is very moist; I wasn't convinced that it would do anything for me as typically I would be taking a cool scope (from an airconditioned house) into a warm, humid night particularly during our wet season (if & when the clouds & rain allow).

Dew formation when just using a standard dew shield was very quick & then had to be defeated with a dew strap which then introduced thermal currents in the tube....

With insulation & dew shield formed by the extended insulation, my SCT & now my Mak (replaced the SCT) go for much longer before forming any dew on the corrector & thus, I don't bother with a dew heater anymore...

As Alex stated, I can pretty much get going at whatever power I want as soon as I am setup...

I've gone from skeptic to convert by seeing the practical gains in insulating my Mak vs letting it cool down...

Cheers
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Old 04-03-2020, 11:36 PM
ecsaow (Evan)
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Hey Carlton & Mirko
Im definitely gonna try Alexanders insulation method, and if I can avoid using a dew heater will be great for me, because if I start using cables and power banks, it all gets a bit much for me and I usually dont end up going out.
Will let you guys know how it pans out, thanks for all the great tips and advice.
Cheers Evan
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Old 05-03-2020, 09:52 AM
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Beware of the Synta 127mm Mak's as there real aperture may be 120mm or less , the 150mm used to be around 141mm but the design has now been addressed to an actual 150mm !

Much talk about this on CN forum .
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Old 05-03-2020, 02:52 PM
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Quote:
Originally Posted by ecsaow View Post
if I can avoid using a dew heater will be great for me, because if I start using cables and power banks, it all gets a bit much for me and I usually dont end up going out.
If the corrector starts developing dew with the dewshield, you can use a hair drier to GENTLY dry it out. Don't go hard with the heat. Minimal heat is all that's needed.

My place is very dewy - vegie patch, turf and big park next to me. Occassionally I need the hair drier. With the Mak this is a lot less often than with the SCT (SCT has a thinner corrector).

I have concerns about dew straps - we fret fuss about about cooling our scopes, and we then start sticking heaters all over the place. Dew heaters can have a place, but their use needs to be carefully thought about and applied. Remember, professional observatories DON'T use heat. Ever. There's other means. I've started experimenting with some of this, and the results are stunning! And not a heating element anywhere!
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Old 06-03-2020, 08:47 AM
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Why not a small (150 or 200mm) Dobson ?


Easier to handle and yet much more aperture and less obstruction. The large obstruction of a Mak decreases contrast in planetary viewing.
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Old 06-03-2020, 10:50 AM
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mental4astro (Alexander)
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Sky', have a read of post No. 7. The OP explains his reasons.

As for the loss of contrast in a Mak, I'm not sure that really is all that applicable. The % contrast difference is questionable if we can actually see it, and not to mention sec obstruction difference is really being all that significant between Newts and Maks, and even SCT's. Different Maks and Newts will all have differences in % obstruction too.

I will say more significant is the optical quality of EACH instrument, regardless of design or even Brand. If all the photons go where they are supposed to, and the physical design of the OTA, (not the optics - two separate things. Here it relates to the quality of internal baffling), these will have a much greater impact on the final image quality & "contrast" than the size of the secondary obstruction. This is from my experience, not hearsay.

I know the optical quality of my 9" Santel Mak is outstanding (Strehl ratio 0.945). It rips strips off just about every SCT and mass production Newt I've looked through. But I've seen through Wavytone's 10" APM designed Mak (same Intes quality optics & same Strehl ratio (within 0.02 of each other)), which has a marginally smaller secondary obstruction, but the design of the internals are totally different, and OMG! What a Goddamn enormous difference in contrast between the two scopes!!! Same EP used in each scope so the EP cannot be called into question for any differences. Secondary obstruction means a lot less than is given credit for.

And this is not to mention comparisons done between high end large Apos with my Santel, Wavy's APM, and the 7" Intes I had, and there is no difference in planetary detail.

Have all the photons go where they are supposed to go (optical and collimation), and the detail will be there - goes for every scope design. As for contrast, I've only seen the same quality of contrast seen in that 10" APM Mak in other reflectors (Newt, Cass, Mak, SCT, whatever) was in two other 10" Japanese made Cassegrains, one a Dall Kirkham Cassergrain and the other a Klevtsov Cass - not to say other reflectors (Newt, Mak, etc) can also have the same quality of contrast.

Alex.

Last edited by mental4astro; 06-03-2020 at 06:15 PM. Reason: Typo
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Old 16-05-2020, 04:08 PM
ecsaow (Evan)
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Just an update for you all. I finally received my SW 127 mak a few weeks ago during the "lockdown", what a revelation, Loving it.

Been using a standard dew shield during these cold melbourne nights, but have just ordered some bubble foil insulation similar to the US type Reflectix, to permantly insulate the scope.
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