Viewing Mars through two very different scopes

[RobertI]

Tonight I thought I'd try viewing Mars with the 102ED-R (plus binoviewers) alongside the C8. With a very dewy night on the cards, I put some dewstraps on the binoveiwer eyepieces (which became unuseable last time due to dew) and the SCT corrector plate. It was very enjoyable switching between the two and teasing out detail from the red planet and interesting to comparing views. Seeing was ok. It is actually very hard to describe the different views through the two scopes, but in summary I would say the 102ED-R with binoviewers was very nearly able to show the same as the C8 in cyclops mode, however the gap apeared bigger when also using the smaller scope in cyclops mode. The appearance of the planet was very different in both scopes but the difference in detail was subtle. Through the 102ED-R it was easy to get a sharp focus on the disc (partly thanks to the lovely focuser). The planet was a light pink and the variations in darkness on the surface very apparent. In the C8 the planet was brighter and whiter. Focus was harder to achieve, the edges of the disc being less sharp, and the clarity seemed to vary from moment to moment far more than in the smaller scope. But certain types of features were easier to see, for example the sharply defined edges of the dark regions was easier to discern as was the polar cap. In moments of clarity there seemed to be a lot more there but hard to get on paper. However I would say the differences between the light and dark regions was more prominent in the 102ED-R than the C8. I felt that the C8 had more to give though and on a night of excellent seeing it would have pulled further ahead in the amount of detail visible. Different experiences, but both extremely enjoyable. Amazing what a diminuitive 100mm frac with binoviewers can achieve though.

Below is my attempt at a sketch, a comparison from Mars Mapper and a pic of the scopes in action.

 

 

Edited November 7, 2020 by RobertI

[John]

Very interesting comparison report Rob and a nice sketch as well.

Thanks for posting it

 

[globular]

Nice comparison and a great sketch 

[ShrewView]

Very good description of the differences in the views and the benefits of using more than one scope 😁.

Nice set up you have there too. Glad you're getting on with the binoviewers, i enjoy mine but the dew last night was awful and I found the eyepieces wouldn't stay clear. Did the dew straps work well with those? Must invest in some for mine if so.

[RobertI]

1 hour ago, ShrewView said:

Very good description of the differences in the views and the benefits of using more than one scope 😁.

Nice set up you have there too. Glad you're getting on with the binoviewers, i enjoy mine but the dew last night was awful and I found the eyepieces wouldn't stay clear. Did the dew straps work well with those? Must invest in some for mine if so.

Thanks  🙂 The dew straps worked really well, I wrapped a long single dew strap around the both bino eyepieces as an experiment and it kept the dew at bay, but did get in the way of viewing as it straddled the gap between the eyepieces - I have a couple of proper eyepiece dew straps on the way. The scopes were dripping with dew by the end but the eyepieces and corrector plate were clear. The refractor lens was also clear without a dew strap thanks to the very long dew shield. 

[globular]

I put a dew strap on my diagonal and the heat keeps the eyepieces clear without any adverse impact on the views and without getting in the way of changing of eyepieces.

Maybe a strap around the binoviewer body, close to the eyepiece end, might similarly provide enough heat to keep the eyepieces clear?

[AstroTim]

Interesting report. I have a C8 myself but have been wondering how the views from a 4” refractor might compare. Did you try the Binoviewer on the C8 to see how that configuration compares too? What sort of magnification were you able to achieve in the C8, and was that similar to what you could achieve in the 102? I seem to be struggling to get much above 226x (9mm eyepiece) with mine in cyclops mode, and only a little more with the Binoviewer (maybe 250x).

 

Tim

[RobertI]

6 hours ago, AstroTim said:

Interesting report. I have a C8 myself but have been wondering how the views from a 4” refractor might compare. Did you try the Binoviewer on the C8 to see how that configuration compares too? What sort of magnification were you able to achieve in the C8, and was that similar to what you could achieve in the 102? I seem to be struggling to get much above 226x (9mm eyepiece) with mine in cyclops mode, and only a little more with the Binoviewer (maybe 250x).

 

Tim

Hi Tim,

I was using around 170x with the binoviewers (difficult to know exactly as I was using a barlow with unknown spacing). I had a zoom on the C8 and went up to a maximum of 250x, but I found the best views were to be had around 170x (again approximate due to use of zoom), coincidentally the same as the binoviewer. I find magnifications beyond 200x rarely yield any extra much of the time, unless seeing is exceptional. I might live in an area of permanently bad setting though! 
 

All magnifications stated are  very approximate, I’ll try a measure the true magnification at some point. 🙂
 

 

[markse68]

Hi Robert, interesting report and lovely sketch  Sounds like the seeing conditions were quite poor and that old saying that larger aperture suffers more in poor seeing must be true from your description! Interesting too that the colours and contrast were better with the smaller aperture. I noticed similar when playing with my toy celestron bird jones thing the other week- it gave a small but sharp disk in a nice dark reddish pink compared to bright very subtly pinky orange in my dob, but i put it down to using lower magnification but sounds like it’s more aperture related from your comparison. I guess it’s just more light captured, brighter image, over saturated eye sensors? and probably why the orange filter can help improve contrast on a larger aperture. But then you’d expect an nd to do similar but I don’t remember that being the case when i was playing with my variable polariser the other week. And the colour is definitely there as witnessed in images taken with large aperture scopes but then i guess they can play with levels like we can’t! Perplexing  🤔🤷‍♂️

Mark

Edited November 8, 2020 by markse68

[Stu]

8 hours ago, RobertI said:

but did get in the way of viewing as it straddled the gap between the eyepieces

Hope it kept your nose warm Robert? 🤣

Excellent report, thanks very much. It matches my experiences with my 4” scopes and the 8” f8. It is only when the seeing stabilises that you really start to see the additional resolution available in the larger scope, but even then, as you say, I find it hard to describe the differences, it’s just like a higher resolution image with more subtle variation visible.

I had some great views early on last night in the f8, unfortunately it clouded over before Mars transited, I reckon it would have been excellent as the setting was good here. Just caught Syrtis Major coming onto the disk.

[RobertI]

40 minutes ago, markse68 said:

Hi Robert, interesting report and lovely sketch  Sounds like the seeing conditions were quite poor and that old saying that larger aperture suffers more in poor seeing must be true from your description! Interesting too that the colours and contrast were better with the smaller aperture. I noticed similar when playing with my toy celestron bird jones thing the other week- it gave a small but sharp disk in a nice dark reddish pink compared to bright very subtly pinky orange in my dob, but i put it down to using lower magnification but sounds like it’s more aperture related from your comparison. I guess it’s just more light captured, brighter image, over saturated eye sensors? and probably why the orange filter can help improve contrast on a larger aperture. But then you’d expect an nd to do similar but I don’t remember that being the case when i was playing with my variable polariser the other week. And the colour is definitely there as witnessed in images taken with large aperture scopes but then i guess they can play with levels like we can’t! Perplexing  🤔🤷‍♂️

Mark

I did think about using some of my coloured filters, but ran out of time. I haven't found coloured filters reveal any more detail, but change the viewing experience as they can highlight certain features. My feeling was that they might be worth a go with the C8, perhaps I'll try this next time out.

[RobertI]

30 minutes ago, Stu said:

Hope it kept your nose warm Robert? 🤣

Excellent report, thanks very much. It matches my experiences with my 4” scopes and the 8” f8. It is only when the seeing stabilises that you really start to see the additional resolution available in the larger scope, but even then, as you say, I find it hard to describe the differences, it’s just like a higher resolution image with more subtle variation visible.

I had some great views early on last night in the f8, unfortunately it clouded over before Mars transited, I reckon it would have been excellent as the setting was good here. Just caught Syrtis Major coming onto the disk.

Thanks Stu. I've not viewed Mars yet using the 6" F8 Newt, so next time out I'll set this up next to either the 4" frac or the C8 (I'm open to suggestions! ). I'm still really amazed by what a decent 4" frac can achieve on planets especially with a binoviewer. I'm going to say something controversial (and very unscientific), but so far for me the binoviewers seem to be adding another inch to the aperture compared to cyclops viewing! 

[AstroTim]

Hi Rob, thanks for the magnification info. No need to spend time measuring, I was only after a rough idea to compare to what I’m achieving through my scope, which seems to be similar. I have seen much higher magnifications being reported with a C8 but have never managed to anywhere near myself. We must have similar local seeing conditions!

 

Tim

[AstroTim]

21 minutes ago, RobertI said:

I did think about using some of my coloured filters, but ran out of time. I haven't found coloured filters reveal any more detail, but change the viewing experience as they can highlight certain features. My feeling was that they might be worth a go with the C8, perhaps I'll try this next time out.

I have tried a moon and sky glow filter and it can tease out a little more detail on occasion (although possibly just when the moon is nearby). I also find that I achieve more magnification when using the Binoviewer with the C8 (Binoviewer with 20mm eyepieces and 1.6x nosepiece barlow is the max I’ve managed), hence my earlier question. I’m beginning to wonder whether it is down to the light being split in the Binoviewer, resulting in less glare from the surface at the higher magnification and therefore more detail visible than in cyclops mode. I am hoping to get hold of a variable polariser at some point to see if dialling down the surface brightness might increase the magnification and detail achievable.

 

Tim

[RobertI]

6 minutes ago, AstroTim said:

I have tried a moon and sky glow filter and it can tease out a little more detail on occasion (although possibly just when the moon is nearby). I also find that I achieve more magnification when using the Binoviewer with the C8 (Binoviewer with 20mm eyepieces and 1.6x nosepiece barlow is the max I’ve managed), hence my earlier question. I’m beginning to wonder whether it is down to the light being split in the Binoviewer, resulting in less glare from the surface at the higher magnification and therefore more detail visible than in cyclops mode. I am hoping to get hold of a variable polariser at some point to see if dialling down the surface brightness might increase the magnification and detail achievable.

 

Tim

I haven't tried the binoviewer in the C8, but will do, should be good. From my calculation you should be getting around 180 - 200x with the C8+binoviewer+20mm eyepieces+1.6x nosepiece. In theory it should be 162x (2032mm x 1.6 / 20mm) but from reading up on this, it looks like using the binoviewers in an SCT increases the focal length to around F12 (as the main mirror has to move closer to the secondary to reach focus with a binoviewer, and the secondary magnifies this change in distance by a factor of 5) so you may be closer to 180x - 200x. What do you think? 

[Stu]

46 minutes ago, RobertI said:

Thanks Stu. I've not viewed Mars yet using the 6" F8 Newt, so next time out I'll set this up next to either the 4" frac or the C8 (I'm open to suggestions! ). I'm still really amazed by what a decent 4" frac can achieve on planets especially with a binoviewer. I'm going to say something controversial (and very unscientific), but so far for me the binoviewers seem to be adding another inch to the aperture compared to cyclops viewing! 

I’m sure others would support your comments Robert. I’ve not used my binoviewers on Mars this year, not totally sure why but I may give it a god next time out. Thinking about it, they won’t reach focus with the Vixen which I’ve tended to use because of the longer focal length vs the Tak. I also enjoy the flexibility of the zoom too to tune to the seeing conditions. I’ll get the Tak setup and give it a go, next time out perhaps, or can try them in the 8” too.

I can only echo you comments about 4” apo scopes though, they can give amazing views and are so easy to setup and use.

[AstroTim]

Hi Rob,

I don’t have an exact figure, and it’s a while since I tried to estimate it, but recall it being between 200x and 210x i.e similar to a 10mm in cyclops mode (I have a non-stock diagonal which increases the light path too). As mentioned on a previous thread, I use the barrel from a barlow to extend the light path a little further, and this gets me to what I would estimate to be a little over 225x, which is more than I have achieved in cyclops mode. I probably can’t pick out any more detail through the bino than in cyclops mode, but find it easier to observe, and therefore the detail is seen more easily. I’d say it’s a similar effect to what you observed between your scopes, where the clarity in cyclops mode appears to vary more than in bino mode.

Tim

[Peter Drew]

I've also been comparing different telescopes observing Mars and have come to similar conclusions.  The main comparison has been between a 16" SCT and its SW 150ED "finder".  In general, the refractor gives a neater, consistently more stable image than the SCT and the colours are more pronounced but at high magnification around 400x the image in the refractor becomes dim whereas the SCT, presenting a larger exit pupil remains more than bright enough.  I tried a whole range of colour filters but all were disappointing.  I've yet to try a couple of the more recommended specialist filters.  Overall, the best image of the night has been with the SCT which is probably to be expected, if only there was that perfect night!  I also have a vintage orange C8 that puts up excellent images, almost as good as the 150ED but noticeably different in presentation.  My experience over the years leads me to believe that there is small incremental difference in planetary detail as apertures increase, visibility of faint DSO's is a different matter.    🙂 

Edited November 8, 2020 by Peter Drew
typo

[RobertI]

18 minutes ago, Peter Drew said:

and its SW 150ED "finder"

🤣

[RobertI]

26 minutes ago, Peter Drew said:

I've also been comparing different telescopes observing Mars and have come to similar conclusions.  The main comparison has been between a 16" SCT and its SW 150ED "finder".  In general, the refractor gives a neater, consistently more stable image than the SCT and the colours are more pronounced but at high magnification around 400x the image in the refractor becomes dim whereas the SCT, presenting a larger exit pupil remains more than bright enough.  I tried a whole range of colour filters but all were disappointing.  I've yet to try a couple of the more recommended specialist filters.  Overall, the best image of the night has been with the SCT which is probably to be expected, if only there was that perfect night!  I also have a vintage orange C8 that puts up excellent images, almost as good as the 150ED but noticeably different in presentation.  My experience over the years leads me to believe that there is small incremental difference in planetary detail as apertures increase, visibility of faint DSO's is a different matter.    🙂 

Interesting comparison Peter, as you say similar experiences but on a bigger scale. Looking forward to trying the binoviewers with the C8 and getting the 6" F8 Newt out at some point.

[bomberbaz]

1 hour ago, RobertI said:

🤣

I have seen it rob, quite impressive although first time I saw it I was like, wow !!

[Merlin]

Small 'scopes are okay for showing planetary details, but for deep sky objects, that's where a bigger 'scope comes into its own.

[Paz]

I've never compared my C8 and 102ED-R back to back but this report sounds similar to my experience. The 102ED-R is easier for getting the focus exactly right and is not miles off in the detail it shows. The C8 is harder work to get the best out of it and requires patience waiting for the spells of good seeing aligned with good focus, and when these moments happen it pulls ahead of the 102ED-R.

I've tried both with and without binoviewers and the main difference for me is just that it's easier to relax and therefore look for longer with binoviewers and therefore see more. I use a glasspath corrector with the C8 even though the C8 could focus without one, it's just to try and keep the C8 mirror as close to its optimum position as possible.

[Paz]

p.s. how do you get a Skytee 2 set up line that to have a two scopes on the same axis instead of using the standard offset second mounting point?

[RobertI]

34 minutes ago, Paz said:

p.s. how do you get a Skytee 2 set up line that to have a two scopes on the same axis instead of using the standard offset second mounting point?

The two scopes don't really line up! Initially I drilled two holes to mount the top saddle on the side (over the hole for the counterweight bar) and the altitude could be adjusted to line up with the other saddle (there are grub screws on the mount which allow this) - this actually got fairly close. However the arrangement you see is slightly different, with a more secure saddle (I didn't trust the one that came with the mount) which slips over the end of the counterweight bar. This doesn't line up so well, but I'm sure I could get it close with some fettling!

Good tip about using the glass path corrector on the C8, I'll bear that in mind.