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Venus on 29th June: results with 100achro/ 120ED

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#1 stanislas-jean

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Posted 02 July 2013 - 01:44 AM

Some observations performed last 29th on Venus
with 2 scopes a 100mm achromat and a 120ED semi apo chineese.
Venus exhibits its polar caps as clear to bright surrounded by a dark collar band.
Except this the general pattern noted remains usual with no specific event collected with the present means.
The vision was altered by the presence of high altitude cyrrus clouds making for the 100mm observation period more difficult as they appear deeper for masking features on planet in comparison with the 120ED.
Anyway,the results are clear:
the 120ED exhibited more contrasty features in white light,substantially less contrasty in red and blue channels than those noted with the 100mm.
It is strange to note such phenomena with an ED scope for which the results would be better theorically.
I had no time for verification of what was appearing with a W11 filter in the 120ED for making comparison with observations done in white light.
On July the 1st same tests were conducted but under pure sky at the same time period. The effect is confirmed with adding the fact that the W11 filter use exhibited the same features observed in white light and still the lost in B and R channels.
My conclusion is the scope is not enough suitable for planet observations.
What can be the reasons ( this is the fifth ED scope for which I noted this on 100, 110 and now 120ED)?
Open to read some answers about.
Stanislas-Jean

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#2 stanislas-jean

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Posted 03 July 2013 - 12:34 AM

So any views about a scope that may influence the results and validity?
Here by poorness.
Stanislas-Jean

#3 krakatoa1883

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Posted 03 July 2013 - 01:26 PM

Hello Stan

I observed through several Synta 120ED scopes and I always found them to be very good planetary scopes although not as contrasty as the 100ED f/9 version. I would say that from this point of view a 120ED should be at least as satisfactory as any good achromat, even through coloured filters. May be your one is defective ?

As far as your drawing is concerned I must confess that I find it too much detailed to be realistic, most of the dusky markings you have reported might merely be a seeing effect. Try to observe with a somewhat larger aperture (say 150 or 200 mm) and darker filters as W38A or even W47. An excellent filter vor visual observations of Venus while still manageable with medium to small apertures is the dark blue from Baader Planetarium. Regds.

Raf

#4 brianb11213

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Posted 03 July 2013 - 02:58 PM

One big issue with short focus refractors is spherochromaticism i.e. shperical aberration not being corrected uniformly across the visible spectrum. This applies to triplets too. The spherical aberration is well corrected in the green / yellow but tends to start to become an issue as the violet or extreme red end of the spectrum is approached.

My WO FLT 110 is actually pretty good in the violet (even down to the calcium K line which is near UV so far as my eyes are concerned) but its imaging potential in the infra red is diappointing. I believe that spherochromatism is the issue. I would not be at all surprised to find that spherical aberration is an issue at the ends of the spectrum in the Synta 120ED doublet objective due to the rather short working focal ratio (focal length 900mm; f/7.5).

#5 stanislas-jean

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Posted 03 July 2013 - 03:37 PM

I donot expect some issue with seeing effects.
There is nothing to do under the conditions of use.
See the link
http://alpo-j.asahik...13/v130620z.htm
for comparison with a short 120 achromat here better than the said semi-apo (120ED is not an apo).
The lacks observed in B and R channels are, on same channels the 100mm achromat allows to see more (here a TAL100mm).
Sothat my conclusion is that these apos are not suitable for use on planets except for getting pleasing views in IL that is.
This is a little disapointing and with regards to the expense done for few (being the fifth apo tested from 100, 110 now 120ED).
I will continue the comparison with the MN127mm Intes and the venerable 154mm newtonian, largely less expensive.

Brian, don't know if spherochromatism can be the answer because when practicing the ronchi with color filter B and R (with a grid of 10lp/mm) spherical aberration is not appearing sensitively on the 120ED. But this is an explanation. I think the residual chromatic aberration in these channels are not negligeable in fact but don't know how to measure this effect with reliability. May be the roddier can bring something and investigate more this.
Tests are continuing. Thanks for your posts.
Stanislas-Jean

#6 krakatoa1883

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Posted 04 July 2013 - 12:42 AM

Stan, it is absolutely NOT possible than a short focus 120mm achromat can perform better that a 120mm ED unless the last is heavily defective. In any case I would not judge their relative performances from your Venus drawings.

Rgds

Raf

#7 stanislas-jean

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Posted 04 July 2013 - 01:00 AM

The problem: it is possible.
That is a fact for me and with the time being I am building the apo figure which is very strange and modifying significantly the structures observed at the ends of the visible light spectrum. You have to invest in expensive ones for recovering this figure.
The short achro a new time is not a matter of chromatic aberration but of surface acuracy rather.
I donot think this present 120ED bd but just its normalfigure with regards the design offered.
I observed on a long period Mars with an antares 1529 with excellent results and better than the 130 apo from WO.
If we take comparison with Mars observable with the present 120ED the results in IL on the la&st opposition would be like this: maria well revealed and clouds revealed confidential with so moderate contrasts. Last opposition was lead by atmospheric clouds activity (EBC) and what with this such OTA? No frankly this is not suitable.
Your analysis is not appropriate.
I found on the net some curves for ED apos, strehl versus wavelength. This is instructive for understanding the figure observed. Don't forget the fact that the observations are conducted here in color channels R, G and B sothat your assessment is not suitable.
Stanislas-Jean

#8 stanislas-jean

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Posted 04 July 2013 - 11:38 AM

I found this kind of results on the net for a super ED152mm.
This is not for the 120ED but should be worst than the graph below that explain the venus observations given.
Stanislas_Jean

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#9 krakatoa1883

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Posted 04 July 2013 - 01:53 PM

The graphics above only shows that the specified objective is better than diffraction limited over a large part of the visual spectrum including both blue and red, which is not surprising for me. It doesn't explain why you have been disappointed by the 120ED in observing Venus unless you can demonstrate that the SR vs wavelength curve of the 120ED is dramatically worse than that, even worse than the curve of a short focus achromat. Anyway, I routinely observe Venus through my 120ED and I can say that it performs fine through deep red, blu and even violet filters.

As this is not the right forum where to discuss the relative merits and demerits of achromats vs ED I suggest you to open a specific discussion in another section (e.g. refractors) where to look for a possible explanation of what you found.

#10 stanislas-jean

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Posted 04 July 2013 - 04:12 PM

I think this is wrong views. Are you vendor?
The merit of the forum is to make parallel between observations and OTA characteristics.
For getting a stehl of 0.80 at 0.5nm and at 0.6nm this is not actually excellent and not suitable.
The 38A filter covers less than the 0.5nm and the 29 filter beyond 0.6nm.
A simple newtonian will do significantly better on that fields by the numbers and by the observations and the 100mm achromat also (see the german site astroforen.de for results got on a 100mm tal in RGB).
Between some theory and the observations that must be conform there are OTA between the 2 ends with flaws involved by design and contruction.
Stanislas-Jean

#11 krakatoa1883

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Posted 08 July 2013 - 04:38 AM

I think this is wrong views. Are you vendor?
The merit of the forum is to make parallel between observations and OTA characteristics.

in the present case this exercise seems very difficult, I find it very hard to believe Venus can have the appearance you give her in your drawings.

#12 stanislas-jean

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Posted 08 July 2013 - 06:00 AM

Presently conditions are appropriate for the exercise with good to excellent seeings sometimes on some late afternoon.
Stanislas-Jean

#13 krakatoa1883

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Posted 08 July 2013 - 06:58 AM

It's no matter of seeing... Are you really convinced that your drawings represent the actual appearance of the planet?

#14 stanislas-jean

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Posted 08 July 2013 - 09:17 AM

it is.
S-J

#15 stanislas-jean

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Posted 08 July 2013 - 09:20 AM

Please have a look on
http://alpo-j.asahik...13/v130706z.htm
since for the 1-4-5-6th last.
S-J

#16 krakatoa1883

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Posted 08 July 2013 - 10:41 AM

It seems that your drawings don't match any Venus drawing or CCD image of the past, present and - probably - future.
Believe me, Stanislas, you have to reconsider your approach to planetary observing unless you want to continue to waste your time.

#17 stanislas-jean

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Posted 08 July 2013 - 12:58 PM

Believe me you have to reconsider your approach too.
Check carefully what is done.
Reference is not to be, even at national commissions, I was in the 80ies.
I think in fact you don't know what is my approach as you said. I saw on your website reports, you waste your time.
The scope test reports found are pure satisfaction.
Sorry.
I stop here this is useless and not bringing something.
Stanislas-Jean

#18 azure1961p

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Posted 08 July 2013 - 08:18 PM

Stan,

The contention here is that there are so very many lines, shades and dashes that to correlate them to a CCD image is not convincing because at least some of the details , real or not will stand as proof in your favor though a good number don't have a correlate at all.

Pete

#19 stanislas-jean

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Posted 09 July 2013 - 12:32 AM

I think you could be the last guy for bringing something here when we see reports of you, apart bla bla.
Sorry for the few.
We are not making on "desk corners".
Still out of concern.
Read again the forum beginning for the subject here.
Stanislas-Jean

#20 Rich (RLTYS)

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Posted 09 July 2013 - 05:39 AM

To All

Keep it friendly. :shameonyou:

Rich (RLTYS)

#21 azure1961p

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Posted 09 July 2013 - 07:25 AM

Stan,

There's no pecking order of whose a viable poster here on this thread. I stated pretty to the point why there was contention here and what the points centered around. I'm actually a good person to comment here maybe not the best but not the last. You need to take a step back.


Pete

#22 David Knisely

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Posted 09 July 2013 - 01:30 PM

These drawings definitely highly exaggerate the width and contrast of any visual detail that might possibly be visible on Venus. Most of the time when I view Venus in eight to ten inch apertures, the disk is pretty much blank except for the slight soft phase shading that is easily visible towards the terminator. The only times that I have seen anything on the disk is when Venus is considerably closer to us than it was late last month, with a phase approaching 50% illumination. Then, I can sometimes see a few very very fine narrow very low contrast wispy markings that seem to flow parallel to each other but overall show some curvature or slight sinuosity sometimes. However, even the slightest seeing variations tend to render them invisible even in a deep blue or violet filter. Most of the time (even under good seeing), I see little to nothing on the planet, so markings are not always present. I observe Venus in the daytime or during bright twilight just after sunset for the most part, as then, it is high enough above the horizon to be in an area of fairly stable seeing. The markings I have glimpsed on Venus are very narrow, wispy, and hard to see even in a 10 inch, so I have some doubts they would be visible in only a 120mm aperture.

I have drawings I made as a beginner in the late 1960's using my 2.4 inch refractor which show a large-scale "Y" shaped patch on the planet when it was in a gibbous phase. I have not seen this repeated since then in my larger scopes, so I have at least some doubts that what I recorded may have been much more than just a visual contrast illusion. Clear skies to you.

#23 stanislas-jean

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Posted 10 July 2013 - 12:20 AM

Next time at your eyepieces for Uranus!
Effectively David the features reported are given with a strongly amplified contrast. Well seen.
Stanislas-Jean

#24 krakatoa1883

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Posted 10 July 2013 - 04:04 AM

The visibility of the dusky markings of Venus atmosphere is a much debated question that can be traced, for example, through the JBAA reports. It is beyond doubt that they can be visible under favourable conditions even through small instruments, however the slightest ondulations of the atmosphere tend to obliterate these subtle features generating illusory details. Their observation and reporting requires considerable skill and experience and should always be considered with much caution. In some instances, however, more contrasty details can be easily seen, this occurred for example during the early spring of 2012 when the visible counterpart of some prominent UV bands could be traced through blue and even green filters.

After almost twenty years of observing and collecting Venus observations for the UAI, it is now my opinion that the visual observer should concentrate most on those details that can be seen with certainty at the eyepiece, that is the phase, the ashen light, the bright caps, the terminator shape etc. leaving the study of the dark bands to the CCD imagery which is more effective at the shortest wavelengths.

#25 brianb11213

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Posted 10 July 2013 - 04:46 AM

The visibility of the dusky markings of Venus atmosphere is a much debated question that can be traced, for example, through the JBAA reports. It is beyond doubt that they can be visible under favourable conditions even through small instruments, however the slightest ondulations of the atmosphere tend to obliterate these subtle features generating illusory details. Their observation and reporting requires considerable skill and experience and should always be considered with much caution. In some instances, however, more contrasty details can be easily seen, this occurred for example during the early spring of 2012 when the visible counterpart of some prominent UV bands could be traced through blue and even green filters.

Agreed. Personally I consider Venus to be a most difficult target to observe visually, any markings which are visible being very subtle and almost impossible to draw without the drawing showing far more contrast than is actually visible.

Smaller apertures might actually have an advantage in tending to have more contrasty images than larger apertures, the contrast gradient being reduced by increased magnification and the eye being overwhelmed by the extra light delivered by a larger objective. Visual observation in daylight is not so effective as diffuse skylight reduces the already minimal contrast. In my experience, anyway.

After almost twenty years of observing and collecting Venus observations for the UAI, it is now my opinion that the visual observer should concentrate most on those details that can be seen with certainty at the eyepiece, that is the phase, the ashen light, the bright caps, the terminator shape etc. leaving the study of the dark bands to the CCD imagery which is more effective at the shortest wavelengths.

This is getting very close to saying that, in this age of advanced technology, visual observations no longer have a value. I'm not sure this is true. At any rate, modern visual observations help to interpret historical visual observations: sure, the eye can be and often is tricked, and this does need to be factored in.






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