Does size matter?

[MJP]

I have a 120mm Celestron refractor and have recently bought a 80 mm Vixen refractor for grab and go. To my surprise I am getting images at least as good from the Vixen as I get from the larger Celestron.

Is that what you might expect?

I rather expected to be able to see less with the smaller scope but I could see strcucture in the Orion nebula two nights ago with the Vixen. Something I have never seen with the Celestron.

Mike

[Odd Dob]

Orion nebula is quite bright so should be able to see it quite easily with either scope.

Try finding some of the fainter Messiers with the 80 mm.

[Stevonator]

I've never had any experience with telescopes, but just from reading I know that the larger the object glass, the better. Especially for small aperture. However on that token your 120 mm scope may pack more than enough power to view the celestial objects you look at. Whilst the 80 mm may just have enough power to view what you look at.

I suppose another factor to chuck into the equation is focal length. You say your vixen can see structure in the orion nebula whilst your celestron can't. That may be down to the focal length, the smaller the focal length, the quicker images get focused and vice versa. So when you try to look at the structure of the orion nebula it may look fuzzy with the celestron as it may not have a great focal length. Whilst the vixen might display the nebula in much greater detail. Every telescope has got unique attributes.

Clear Skies

Steve

[spaceboy]

What I have found is unless you do a side by side comparison of the two scopes it is hard to make an accurate assessment of there performance. Seeing conditions vary so much night to night and the temperature of the OTA's play a large part also. You may find that the night you tried out the 80mm the seeing and transparency of the night sky was more favorable than maybe it was the last time you used the 120mm. The 80mm would also cool a lot quicker than the larger 120mm allowing it to perform better sooner. You also have to take into consideration the focal lengths of each scope as exit pupil can also play tricks with you perception. While you may be using the same EP in each scope the exit on the one scope may allow you eye to see more light and subsequently more detail can be seen.

[John]

I put my ED120 refractor side by side with my Vixen ED102 refractor on Jupiter last night and used the same magnification in both scopes - 150x. At 1st glance the views were very similar but it was in those moments of good seeing that the ED120 pulled out those subtle details in the surface features that the 102 was only hinting at. I then turned them on M81 and M82 and the "gap" was a bit wider as the additional light grasp of the 120 enabled more contrast and surface brightness to be seen on each galaxy.

You really do need to compare things "back to back" though under the same conditions, with the same magnification, same quality eyepieces etc to draw an accurate comparison, as Spaceboy says.

[ronin]

Aperture simply captures more light. The quality of the optics, mirror or lens, gives the final image quality

It sounds as if the 80 has simply gone through a better design or the components used are a better combination. May even be as simple as a cemented lens compared to a seperated lens.

The glass in the 80 may not be ED but could be a lower dispersion then the one in the 120, also at 120 there will be greater spherical aberation present that will cause a poorer image. That bit from 40-60mm out fom the centre will contribute a reasonable amount.

The human eye is more sensitive to contrast then intensity. So the 120 could have less contrast then the 80 and the image detail will not be as obvious.

The 120 will collect about twice as much light, however the eye will not "see" objects that are half as bright. The eye isn't linear.

So several possible reasons. Where the 80 should "fail" is on the much fainter DSO's. However 80mm is a reasonable size.

[umadog]

You also have to remember that a telescope won't make objects brighter, it will just allow you to magnify more. If the two scope are set up side by side with eyepieces yielding the same exit pupil sizes then the views will look equally bright. Probably, however, you larger aperture scope has a longer focal length. Consequently, the object will appear bigger with the same exit pupil in the larger scope.

Contrast is affected by optical quality. I believe Vixen have a particularly good reputation for optical quality, so it's possible you're seeing that in action. I don't know much about refractors, however, so I couldn't tell you what would cause that.