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Maksutov vs Newtonian

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#1 CHRISTOS

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Posted 21 June 2004 - 06:23 AM

Hi to all
Last Saturday night I was out for observing with a friend. He had a 130 mm Newtonian Skywatcher - I had an Intes Micro 500 Mak (127mm). What I (and he) noticed after a brief comparison on well known objects (mainly globular clusters) was that the images thru the Newtonian were fairly brighter than the ones from the Maksutov. Because I am a beginner, I cannot understand if this generally applies for all Mak Vs Newtonian scopes (with same aperture), or it has to do with this specific Mak : defected/miscollimated/dust on mirror etc.
Can anybody help ?

#2 bierbelly

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Posted 21 June 2004 - 06:37 AM

Hi to all
Last Saturday night I was out for observing with a friend. He had a 130 mm Newtonian Skywatcher - I had an Intes Micro 500 Mak (127mm). What I (and he) noticed after a brief comparison on well known objects (mainly globular clusters) was that the images thru the Newtonian were fairly brighter than the ones from the Maksutov. Because I am a beginner, I cannot understand if this generally applies for all Mak Vs Newtonian scopes (with same aperture), or it has to do with this specific Mak : defected/miscollimated/dust on mirror etc.
Can anybody help ?


The Mak will lose more light due to the meniscus lens, which isn't present on the Newt.

#3 wilash

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Posted 21 June 2004 - 06:50 AM

I assume you were comparing the scopes at the same powers. If the Newtonian was working at a lower power the images will be brighter.

If the powers were the same, the problem is with transmission. Your scope has two extra componants - the miniscus and diagonal. The extra glass and mirror will absorb and scatter light. (Not using a the diagonal and viewing straight through may make the views brighter.) This is not a defect. This will probably be the same compared to other Newtonians. It really depends on the efficiency of the optics.

Unless your scope is really dirty, dust will not dim the views. If it is that dirty, it should affect the images as well.

#4 CHRISTOS

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Posted 21 June 2004 - 07:08 AM

Thank you all very much
Wilash yes, the powers used were similar. The difference between the scopes was not what I (a novice) expected, for example the Mak diagonal is advertised as 96% reflective, not to mention price/origin of the products etc.
By the way, how could somebody clean the dust from inside a Mak scope ? If I remember well, you also have the same scope too.
Thanks again.

#5 wilash

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Posted 21 June 2004 - 07:45 AM

Yes, I have the M503/M500. Simply take off the front miniscus cell. Mount the scope so you can use two hands to remove the cell and change the orientation of the scope.

There are several screws around the end of the tube. Take them out. Carefully slide the black cell holding the minicus and secondary off the front of the tube. It will only rotate slightly in the tube as there in an obstruction caused by the weld of the tube. So pull the cell straight out.

Tip the tube upside down so when you blow the dust out it falls out of the tube. Also turn the tube around and remove the rear cap and blow the dust down the secondary baffle (from the inside or the scope, not the back). Also blow off any dust in the secondary.

Replace the cell. It will only go back in the one orientation. There is a piece of steel used in the bottom side of the tube that is used to weld the tube together. A notch in the cell goes over this piece of steel. The cell lines up very well in my scope and I did not need to collimate the scope afterwards.

I have only used a blower to remove the dust. I have not touched any of the internal optical surfaces. The coatings on the outside of the miniscus are soft, I assume the internal surfaces are too. DO NOT DROP ANYTHING. Good luck.

Sorry if this is too detailed. The first time I did this I was a little nervous.

#6 CHRISTOS

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Posted 21 June 2004 - 08:30 AM

Many thanks wilash
especially for the details !!!
Is it too much to ask what did you do to collimate the scope ?
Thanks in advance

#7 wilash

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Posted 21 June 2004 - 08:46 AM

My scope was collimated by the retailer (ITE) when I bought it. It has not needed collimation since. I check it from time to time, but so far I have not had to adjust it. I have instruction somewhere. I will look and post them tomorrow.

#8 Mike Hosea

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Posted 21 June 2004 - 03:04 PM

Cleaning out dust is not likely to make a noticeable difference, except for the phenomenon that makes me think my car runs better after I wax it.

Christos, there are two issues. One is actual transmission, which will be lower for the Mak, and the other can be a slight color tinting, also tending to be more noticeable for some Russian-made Maks for whatever reason (as I recall, Markus Ludes has said that it was due to the type of Russian glass used in the corrector). So expect the Mak to be slightly dimmer, but also make sure you are comparing brightness of faint objects, not bright ones, to see the real difference in transmission.

#9 bierbelly

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Posted 21 June 2004 - 09:03 PM

Cleaning out dust is not likely to make a noticeable difference, except for the phenomenon that makes me think my car runs better after I wax it.


What are you suggesting?

#10 wilash

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Posted 21 June 2004 - 09:16 PM

Mike, you have never owned a Russian scope or your had quality control issues that someone overlooked - dirt is not supposed to be an option (it comes standard). I opened mine up to clean, not because I thought the metal filings () inside would effect the images, but because they could damage the optical surfaces.

And my car DOES run better after a waxing!

#11 bierbelly

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Posted 21 June 2004 - 09:30 PM

And my car DOES run better after a waxing!


Precisely!

#12 Mike Hosea

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Posted 21 June 2004 - 11:37 PM

Okay, okay. I stand corrected. :grin:

#13 CHRISTOS

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Posted 22 June 2004 - 03:50 AM

Mike
what do you mean "compare faint objects" ? Objects barely visible thru the Newtonian scope and invisible to the Mak ?
If I use a better diagonal, will the difference justify the extra cost ?

(should I wax my bike also?)

#14 jrcrilly

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Posted 22 June 2004 - 03:58 AM

I dunno; it takes a fair amount of difference in light levels to be easily detectable. Moving up from a 96% reflective diagonal won't do it. Neither should adding a corrector or a small central obstruction. If the magnifications were similar then different eyepieces were surely in use - could those be the difference?

#15 CHRISTOS

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Posted 22 June 2004 - 04:44 AM

jrcrilly
yes, the Mak had Celestron Plossls while the Newtonian had Skywatcher Kelners. I don't know the real difference between them, but my wide angle Kelner -supplied by Intes Micro- is not as sharp as my Plossls.

#16 wilash

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Posted 22 June 2004 - 06:13 AM

I'm sorry I don't have experience with collimating the M503, but I can give the procedure in the manual.

Cool down the scope. Center a bright star in the center of the field and defocus the image. Use a 6mm to 12mm eyepiece. If the image is not round, then the scope needs to be collimated.

Adjust the secondary with the three screws under the cap. The screws need only be turned a tenth of a turn to affect the collimation. If the screws are tight, do not force them. Back out all three equally and continue to adjust collimation. The image will move to the edge of the field as the scope is collimated.

The primary should then be adjusted to return the image to the center of the field. There are two sets of three screws set 120 degrees apart. The larger outer screws are "pull" screws. The small inner screws are the "push" screws. Loosen the 3 push screws and then adjust the three pull screws to colimate the scope. After adjusting the primary, tighten the push screws hand tight. Do not over tighten the screws. If the pull screws do not move the mirror, loosen the push screws and continue.

Continue to adjust the secondary and primary until the image is circular with a black dot in the center. The image should be the same on both sides of focus.

I hope this is helpful.

#17 Mike Hosea

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Posted 22 June 2004 - 12:09 PM

By the "comparing faint objects", I was just trying to steer you clear of a pitfall. I just meant to compare what you really care about when it comes to transmission, i.e. faint objects like galaxies and nebulae. Obviously, finding a faint star that you can see in one scope and not the other is a smoking gun, but I wasn't suggesting anything that serious (or arduous and boring). For a subjective idea of how transmission compares, it doesn't have to be on the threshold of visibility, just not bright stars or a planet. The point is that a color shift with bright objects can be misleading. If you compare with a faint obect, you won't be distracted by any color shift (because you can't see the color anyway), and you can concentrate on the actual brightness difference. As I read your original question, however, it seems that you were using globular clusters. That's fine.

I had a similar experience, by the way, when a neighbor brought over an 8" Newtonian when I had an 8" SCT. The Newt sure seemed brighter to us.

#18 CHRISTOS

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Posted 22 June 2004 - 01:29 PM

Mike, I will try the comparison you said, using the same type of eyepieces this time.
Thank you very much guys for your advices.


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