ED100 and Skymax 127 - too big a difference?

[orley]

Hey,

For a couple of years now I've been thrilled with the views my ED100 has given, crisp, clear and contrasty to a delight. That it could do with more aperture I'll reluctantly admit, which has led me to contemplate bringing in a 10" dob...but that's a tale for another day. For now know that I've had not one moment of regret.

Back in April I picked up a second-hand Skymax 127, more out of curiosity of comparative views with the ED. I've used it in anger on several nights now on targets such as the Moon, Saturn, Mars, M13 and M57. To be honest I've been rather...underwhelmed.

I like the mak. I like its size, it's build, its ability to absorb the magnification I chuck at it and yet it leaves me feeling that things I love about the ED are missing. I spent some time checking the collimation (which seems fine), but each time I use it I come away more than a touch disappointed.

Now, I know the mak is not far off a third of the cost of the ED, but I was expecting a closer match. Has anyone else owned both and felt the same? Or am I expecting too much? I'm using the same eyepieces (BST Explorer and Pentax) in both, the only difference being the diagonal - 2" dialectric with 1.25" adapter with the ED, stock 1.25" diagonal with the Skymax.

Or is it just me? Apologies to any Skymax owners whom this post may upset - everything is subjective. I'm just wondering if there's something amiss...

Thanks in advance.

[nightfisher]

Not had a chance to try both these scopes, i do have the larger 150 mak, and a pretty good scope it is, bear in mind the 127 vs 100ed, the mak has a central obstruction that robs it of some thing like 30% aperture, and an unobstructed frac will have a better contrast

[dweller25]

I have also had both these scopes and used them for visual planetary.

When each scope was fully cooled down the 100ED outperfomed the 127 Skymax.

This is normal - the 127 has a 40mm obstruction so contrast transfer is roughly the same as an 87mm refractor (127-40 = 87mm)

However I have read that the primary mirror in the Skymax is actually only 120mm so if this is correct then contrast transfer is the same as an 80mm refractor.

Contrast transfer is very important for the planets and this is probably the effect you are seeing.

To beat the 100ED you would need a clear aperture of 120mm to see any useful difference - for example the Skymax 180 has a 58mm obstruction giving a contrast transfer of 122mm.

I bought a Takahashi TSA102 and compared it to the 100ED - the Tak was slightly sharper and slightly more contrasty - however the price difference was not slight !!!

The 100ED is excellent value for money. 

[Macavity]

... the mak is not far off a third of the cost of the ED...

A good guide to astro equipment generally?

I once did a daylight comparison of a MAK127 with an ST102, on a Giro III dual mount.

The 'Frac was far more "contrasty" and initially impressed! But it was much more "blurry"

than the MAK - Perhaps beyond differences attributable to chromatic aberration alone?

I found that (terrestrially notably) MAKs give rather "muted" images? On the other hand,

they do give fairly text-book diffraction patterns and work to high power. I suspect, once

you've subtracted a bit from the MAK127 (sub?) aperture, it is more a "120 mm" scope"?

Plus you have the central obstruction, the mirrors are not 100% reflective etc.

As a fellow '150 owner, I might echo one idea? IF you can afford it, go for a MAK 150?

Not often considered, but they retain many of the "general purpose" features of a 127,

but without the more specialist "planetary scope" features (virtues!) of the MAK180.

Aside: For planetary *imaging*, I found my MAK150 quite hard to focus manually.

But it is significantly improved by addition of a Crayford-style *electric* focusser. 

MAKs benefit generally from a "bit of fiddling about" to get the best out of them?

Newts even more so! There's not much you can (need to) do with an ED 'frac? 

[orley]

Thanks all. What you guys are saying makes sense.

Ah well, time to offload the mak methinks...

[ronin]

For all that is said it takes a fair bit to beat a decent refractor, yet it always seems to be the last thing suggested to anyone.

They seem to operate in a manner that is well suited to the response/operation of the eye, which is itself a refractor.

[lensman57]

For all that is said it takes a fair bit to beat a decent refractor, yet it always seems to be the last thing suggested to anyone.

They seem to operate in a manner that is well suited to the response/operation of the eye, which is itself a refractor.

I have both of the scopes mentioned and a couple of fast Newts of 6" and 8" aperture. To my eyes and also in imaging I find that the mirror type scopes have a flat feel to them, the EDs and Apos seem more three dimensional but one important factor is the very flat field of the Mak, the others all suffer from a curved field.

A.G