Hi,acc
Congrad.Want to ask a few technical things--How does this compare with the ordinary nagler;pentex XW;or the meade 4000 series eyepieces?Besides having a wider FOV,is it still tack sharp at the edge?of the field and does it show the same slight yellow colouration at the field edge as of meade 4000 series.Also will it tilt the balance of your 12+ ins Dob and with it do you still need a coma corrector with high f ratio Dob?Thanks.
13mm Ethos
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superiorstream
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acc
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Hi Chia
I have only used the ethos once with my WO 110mm refractor f6 refractor. I would say its sharp to the edge. I am not bothered with a bit of colour at the edge of the FOV, so never checked any of my eps for this effect.
I prefer the meade 4k to the nagler 13mm as it does not impart a yellowish tone to the image like the nagler does.
I do not like XWs at all due to their pronounced field curvature. Its annoying that I can't get the whole of its relatively narrow FOV to snap to a focus at the same time.
No the ethos won't topple my portaball. Only my 2lb+ 28mm UWAN have a tendency to do that at low elevations.
Coma is an issue for me only with low power ep like the 28mm UWAN. I won't be using a coma corrector with the ethos.
croys, chee yiun, pls see my sale thread. thanks.
I have only used the ethos once with my WO 110mm refractor f6 refractor. I would say its sharp to the edge. I am not bothered with a bit of colour at the edge of the FOV, so never checked any of my eps for this effect.
I prefer the meade 4k to the nagler 13mm as it does not impart a yellowish tone to the image like the nagler does.
I do not like XWs at all due to their pronounced field curvature. Its annoying that I can't get the whole of its relatively narrow FOV to snap to a focus at the same time.
No the ethos won't topple my portaball. Only my 2lb+ 28mm UWAN have a tendency to do that at low elevations.
Coma is an issue for me only with low power ep like the 28mm UWAN. I won't be using a coma corrector with the ethos.
croys, chee yiun, pls see my sale thread. thanks.
We do it in the dark...
Portaball 12.5"
Takahashi Mewlon 210
William Optics 110ED
...and all night long!
Portaball 12.5"
Takahashi Mewlon 210
William Optics 110ED
...and all night long!
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superiorstream
- Posts: 1501
- Joined: Mon Nov 03, 2008 4:45 pm
Hi,acc
Thanks for the answer;and now I know the XW are not that good performer.Surprising to learn that nagler has that yellow tint too.;but not too surprised as forum in solar obs indicate that cemax perform better in the colour issue.Already put myself 2nd or 3rd in the Q for the 4000 series 14mm EP.Thanks.
Thanks for the answer;and now I know the XW are not that good performer.Surprising to learn that nagler has that yellow tint too.;but not too surprised as forum in solar obs indicate that cemax perform better in the colour issue.Already put myself 2nd or 3rd in the Q for the 4000 series 14mm EP.Thanks.
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Canopus Lim
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Regarding the yellow 'tint' (which connotes subtraction), it is not a tint but rather one can say that it is subtely 'warmth' and the reason is that some of the glasses used in the design has higher transmission in the red colour; these glasses are high index and high dispersion and they tend to have higher transmission in red. High index glasses are needed to allow the Nagler to perform very well even in fast scopes.
Some people think that 'warmth' eyepieces and telescopes have lower transmission. This is false as warmth is how our eye perceives it. If the eyepiece has peak transmission towards red, the eyepiece will look warmth. If the peak transmission is at green, it looks 'neutral'. It does not depend on the real transmission of the eyepiece. A 40 percent transmitting eyepiece can be 'cool' bias too if it is not coated at all. This is analogous to a 'warmth' fluoresecent lighting compared to a 'cool' fluorescent lighting. It does not mean that the 'cool' fluorescent lighting is always brighter than the 'warmth' fluorescent lighting as it depends on the wattage (for eg. transmission in this case).
From data on the transmission of the Nagler eyepieces and from comparing other eyepieces, it is pretty good, ranking as good or better than simple orthoscopic designs (like Volcano flat tops or other generic plossls). It is only slightly less good than the premium high end planetary orthoscopic eyepieces.
Also this slight warmth can be seen if one is viewing the moon or planets. However, one notices that only if he compares a 'cooler' eyepiece. For DSOs which tend to be grey in colour, there is no 'warmth' discernment at all. Then at the end of the day which eyepiece is 'neutral'? That is pretty subjective too.
Some people think that 'warmth' eyepieces and telescopes have lower transmission. This is false as warmth is how our eye perceives it. If the eyepiece has peak transmission towards red, the eyepiece will look warmth. If the peak transmission is at green, it looks 'neutral'. It does not depend on the real transmission of the eyepiece. A 40 percent transmitting eyepiece can be 'cool' bias too if it is not coated at all. This is analogous to a 'warmth' fluoresecent lighting compared to a 'cool' fluorescent lighting. It does not mean that the 'cool' fluorescent lighting is always brighter than the 'warmth' fluorescent lighting as it depends on the wattage (for eg. transmission in this case).
From data on the transmission of the Nagler eyepieces and from comparing other eyepieces, it is pretty good, ranking as good or better than simple orthoscopic designs (like Volcano flat tops or other generic plossls). It is only slightly less good than the premium high end planetary orthoscopic eyepieces.
Also this slight warmth can be seen if one is viewing the moon or planets. However, one notices that only if he compares a 'cooler' eyepiece. For DSOs which tend to be grey in colour, there is no 'warmth' discernment at all. Then at the end of the day which eyepiece is 'neutral'? That is pretty subjective too.
AstroDuck