Opinions? Premium 8" vs Consumer 8" F6 vs SCT

[kayheem]

Hi all,

Having looked through a premium 8" ( 8" Portaball) and an SCT, I was wondering where all 3 stand when compared head-to-head.

If the 8" premium reflector is 100 points (for reference), how many points would a consumer 8" F6 dob and a 8" SCT score?

That will help me to see if it is worth the hassle to switch to a consumer 8" dob.

Thanks!

[VinSnr]

Hi all,

Having looked through a premium 8" ( 8" Portaball) and an SCT, I was wondering where all 3 stand when compared head-to-head.

If the 8" premium reflector is 100 points (for reference), how many points would a consumer 8" F6 dob and a 8" SCT score?

That will help me to see if it is worth the hassle to switch to a consumer 8" dob.

Thanks!

consumer 8" f/6 at 90%
8" SCT at 80%

Assuming singapore skies condition and only view at the eyepiece is considered.

[Canopus Lim]

In terms of optical quality:

An ideal newtonian scope would have a Strehl=1.0. A premium newtonian (especially an 8" f/6) will usually have strehl>0.95 (so called 95 percent or more). A commerical newtonian will usually have a wide range of strehl values and depends on sample. It would usually lie between 0.8 to 0.90 strehl ratio.

Hence optically the commerical newtonian will provide 80 to 90 percent of the performance of a premium scope. However this only got to do with the figure (shape) or accuracy of the parabolic mirror. The premium optics will usually be smoother (since hand figured and more time spent on each mirror) and hence scatter less light. Also premium scopes have high reflectivity and surface flat secondary mirror which will increase the light througput. Some premium scopes have both high reflectivity primary and secondary mirrors.

Mechanically, the premium scopes are better in terms of damping time and movement. However, the total cost of a premium scope is many times more than a commerical newtonian. Whether it is worth the cost is up to you to decide. In optics, a few more percent improvement usually means many times more expensive.

For SCTs, their optical figure usually tends to be less than satisfactory since it is rather difficult to make a SCT having complex aspheric surfaces. Not to mention the big Central Obstruction, it will reduce the contrast on planetary features. They tend to have more optical 'problems' than Newtonians and it is a bigger gamble to get a better sample than a Newtonian.

[kayheem]

Yes, I am only referring to the view at the eyepiece when considering the scoring.

I am not looking at the mechanical qualities.

Thanks!

KH

[weixing]

Hi,
Assume under normal seeing condition:
Planetary:
Consumer: 90%
SCT: 80%

DSO
Consumer: 95%
SCT: 90%

Just my S$0.02.

Have a nice day.

[ariefm71]

since no mention if the sct is consumer or premium, i'll go with 8" tsc225 SCT any day over the consumer newt

[acc]

If I may borrow Weixing's post since its so nicely presented 8-)
Assume under normal seeing condition:
Planetary:
Consumer: 90%
SCT: 70%

DSO
Consumer: 95%
SCT: 80%

[rlow]

Frankly I have seen excellent 8" SCT as well as excellent 8" consumer newt, though these are the minority, so the quality does varies among the mainstream brands. If you are lucky to get a excellent consumer scope, do thank your lucky stars, as most of the time you may just get a run-of-the-mill quality scope or even a lemon.

Hence I find it difficult to rate consumer scopes at 90% or 80% etc, though the figures stated earlier are somewhere correct within the range. The important difference is that a premium scope is definitely 100% excellent; ie, it will not be run-of-the-mill or a lemon.

Secondly such difference in say 10% is subjective as some people with experience do see the difference whereas others don't.

Thierdly, even for people who see the difference, the next question is whether you are willing to pay much more (usually more than 2x) for a slight improvement.

For me, the answer is yes, I see the difference and I am willing to pay to get a guaranteed premium product that I would use for my lifetime. So I would go for that premium 8" dob.

Btw, you mention '...switch over....' do you already have a premium 8" dob?

[acc]

Agree with Rich but also, at the risk of offending SCT owners, my experience is that the large central obstruction and multiple reflecting services of SCTs are a very severe handicap. So when you compare an "excellent" SCT to a run-of-the-mill commercial newt/dob, the newt still comes out noticeably ahead in terms of contrast and light throughput.

[Meng Lee]

I admit I don't have that much experience as many of you do here. So I will just say my suggestion.

If transportation is not much of a problem, a good big Dob will serve you very well. You can try to get a large aperture Dob for the price of 8" SCT and get better views and large aperture.

I suggest the Meade lightbridge 12" Dob. Big aperture do wonders!