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Review of The New 5mm and 7mm Nagler Type 6 Eyepieces
|Eyepiece||Apparent Field of View||Eye-relief||Approx. Cost|
|TeleVue Radian 6mm||60 degrees||20mm||$228|
|TeleVue Nagler 7 Type 6||82 degrees||12mm||$280|
|TeleVue Nagler 7 (type 1)||82 degrees||10mm||$190|
|TeleVue Radian 8mm||60 degree||20mm||$228|
Telescopes used for this comparison:
Right: TeleVue 7mm Nagler Type 6 eyepiece (at left) next to original design 7mm Nagler eyepiece. (73,412 bytes)
I have owned the Nagler 7mm (type 1) eyepiece since 1996. This old timer provides about the maximum magnification that my 60mm refractor and 18" Dobsonian can handle under Maryland skies. I still use this eyepiece with these two telescopes regularly. I also use this eyepiece on occasion with the two apochromatic refractors. However, in recent years the 6mm and 8mm Radians often rule over the older Nagler because I need glasses to read my star charts, take notes, and draw what I observe. Keep in mind that my astigmatism does not bother me when using a short focal length eyepiece like the 7mm Nagler -- but it is the hassle of having to take my glasses on and off that gravitates me towards using the Radians over the older Nagler.
It is often claimed that just because you do not need your eyeglasses at the telescope that there is no draw back to using an eyepiece that requires you to remove your eyeglasses. This is just not true in my case and I suspect a lot of other people as well. If you need your eyeglasses to read your star charts or take notes be aware that you will enjoy an eyepiece that you can use with your glasses on over an eyepiece that you can't. Until someone comes out with dew-heaters for eyeglasses -- I will continue to keep mine on while observing.
The 7mm Nagler type 6 is half again larger than the older type 1 but appears to weigh about the same. The new Nagler type 6 has increased the eye-relief from 10mm (on the type 1) to 12mm. This still is not enough eye-relief for those who wish to use eyeglasses to get the full wide field effect. Without glasses, I find that both the 10mm eye-relief and the 12mm eye-relief are comfortable to use, with a slight preference going to the 12mm eye-relief of the new type 6. With my eyeglasses on, the 82 degree F.o.V from the new 7mm Nagler type 6 (and also the 5mm Nagler) is reduced to that of an eyepiece with approximately a 50 degree F.o.V.; however, for an observing buddy of mine who also uses eyeglasses the reduction of the F.o.V. of the new Nagler type 6s were about equal to that of a Radian (approximately 60 degree F.o.V.).
The new Nagler type 6 has a slightly larger "effective" field stop (9.7mm) than the type 1 (9.4mm). Effective is stated because the design of the eyepieces is such that a simple mechanical measure of the field stop diameter can not be used in calculating the true field-of-view. The new 7mm Type 6 will provide, very slightly, a larger true field of view than the previous model. This increase in the true field of view, if noticed at all, would only occur with telescopes of very short focal lengths. For example, in my Dobsonian the actual F.o.V. difference between the type 6 (0.27 degrees) and the type 1 (0.26 degrees) cannot be detected. However, in the TeleVue 85 because of its shorter focal length the actual F.o.V. for the type 6 (0.93 degrees) and the type 1 (0.90 degrees) could just barely be detected during testing.
Both the type 6 and the type 1 are well corrected eyepieces across the entire field-of-view. I used stars both in focus and out of focus to test this. If one Nagler was sharper than the other it was below what I could detect. I hate testing Naglers to see if any distortion is present along the edge of the eyepiece because you have to hold your eye at such an unnatural angle just to see the edge, and I am never sure if it is just the eye that creates those fleeting distortions. From a pragmatic point of view when observing the night sky both 7mm Naglers are distortion free right to the edge of the eyepiece. Wonderful!.
The real difference between the two 7mm Naglers is that the new Nagler type 6 produces a cleaner image. I take good care of my eyepieces so I do not believe that wear on the 5 year old type 1 was an issue. The differences in clarity, although subtle, could be detected in all four of the telescopes tested. This was most evident by defocusing colored stars so that the blurred images become larger and dimmer until a difference between one eyepiece and another can be made based on its ability to hold the deformed star's color. This is one cruel unforgiving test for an eyepiece. The new Nagler type 6 was the clear winner.
Testing the 6mm and the 8mm Radians against the 7mm Nagler type 6 was difficult because of the differences in magnification. Of all my telescopes this difference in magnification is least pronounced in the TeleVue 85 refractor so most of the comparison was made using this telescope. After using a number of double stars (including Albireo, Alpha Herculis, the Double-Double), the moon (including the edge illuminated only by Earth shine), Mars, and a half dozen deep sky objects -- I gave up. I could not see any differences between the Nagler and the Radians except for the expected F.o.V. versus eye-relief trade off. As far as I could tell on Mars the established wisdom that Radians are better for the planets than Naglers does not hold for the new 7mm Nagler type 6.
If viewing globular cluster M5 through an 18" Dobsonian using the 7mm Nagler type 6 (294x) doesn't bring you to tears then you should seriously consider taking up bass fishing as your main hobby.
CONCLUSIONS: The new 7mm Nagler type 6 eyepiece is wonderful. It has no faults that I can see. If you are looking for a high end, best that money can buy eyepiece, in the 7mm range, then I fully expect that this is the eyepiece that you will end up getting.
RECOMMENDATIONS: Here are my personal, very unqualified recommendations on the new 7mm Nagler type 6 eyepiece:
If you already own the type 1, sorry but the type 6 is better; however learn to live with it, they are very close and it is probably not worth it to upgrade.
If you do not already own a Nagler 7mm eyepiece and want to buy one -- buy the type 6 over the older type 1 -- even though it will cost you about $60 more.
Normally, if you need, or wish, to wear eyeglasses go for either a 6mm Radian or 8mm Radian. [This rule is not set in stone. Some may find that when using the new 7mm and 5mm Naglers with glasses (because of the 12mm of eye-relief) that the reduced F.o.V. with glasses is close to that of a Radian's total F.o.V. with or without glasses. If this is the case then I would recommend the new 7mm Nagler over the Radians since you will always have the option of still wearing your glasses with a F.o.V. equal to that of a Radian or removing your glasses and enjoying the full 82 degree field of view that only a Nagler can provide.]
REVIEW: THE NAGLER 5MM TYPE 6
Eyepieces used in the comparison were:
|Eyepiece||Apparent Field of View||Eye-relief||Approx. Cost|
|TeleVue Nagler 4.8mm (type 1)||7mm||$155|
|TeleVue Radian 5mm||60 degrees||20mm||$228|
|TeleVue Nagler 5mm Type 6||82 degrees||12mm||$280|
|TeleVue 3mm-6mm Nagler Zoom (at 5mm)||50 degrees||10mm||$380|
Telescopes used for this comparison:
Left: TeleVue 5mm Nagler Type 6 eyepiece (at right) next to original design 4.8mm Nagler eyepiece. (87,208 bytes)
The night is clear, clean, and dark. V-aquilae is a delight to behold. It is so red. Not the orange-color that forms from the low surface temperatures of so called red giant stars like Betelgeuse, Antares, and Aldebaran but the intense deep red of the tainted atmosphere of a carbon star. In a well corrected apochromatic refractor such as the 155mm AP at high power this star appears as a brilliant point of blood fixed against the black face of eternity itself. So what is wrong with me? Instead of enjoying this wonderful star as any normal amateur astronomer would -- here I am looking at it out of focus, barlowed absurdly at nearly 100x/inch of aperture, looking for the most subtle of differences between two, as near perfect eyepieces as you are ever going to find -- the 5mm Nagler and the 5mm Radian. This reviewer has got to get a life; whatever I am doing with an out-of-focused v-aquilae, it is not astronomy. This is not the best use of my time under a dark sky.
I enjoyed the 4.8mm Nagler for years. In its day, it set a new standard for short focal length eyepieces under 6mm. But times change. Radians dealt it a near fatal blow when they entered the market and I believe the 5mm Nagler type 6 will finished the job. Unlike the old and new 7mm Naglers, which when compared were at least close in testing, the cleaner image and much improved eye-relief of the 5mm Nagler sets it way apart from the old 4.8mm. The 4.8mm Nagler's main draw back was that the 7mm eye-relief (always seemed shorter to me) robbed me of the Nagler space walk feeling that I enjoyed with his other 82 degree F.o.V. eyepieces. I have heard it said that the 4.8mm is a lower cost alternative to the 5mm Nagler. It is not. With the 5mm Radian and the 5mm Nagler both currently available I can see no reason (including cost) for anyone to purchase a 4.8mm Nagler new.
Company Seven has already posted my article Review of the new Nagler 3mm to 6mm Zoom. This is really one impressive eyepiece. At the 5mm setting it is as clear and sharp as either the 5mm Radian or the 5mm Nagler. The only compromise is that it can't give you a Nagler's or even the Radians' F.o.V. or can it provide the Radian's ability to use eyeglasses (eye-relief). But if you are in the market for a 5mm eyepiece don't rule out the Zoom too quickly because there are some unique advantages in owning this little eyepiece (see the Zoom review).
Trying to find if there are differences between the 5mm Radian and the 5mm Nagler except for the trade off between eye-relief and field-of-view was not successful. Both eyepieces with the TeleVue 85 refractor easily split Izar clean with black space in between at 120x -- impressive! Under working magnifications with both apo refractors I could not see any differences between the two eyepieces using a series of double stars, deep sky objects, the moon and Mars. Even using the 155mm Starfire during the defocused star test mentioned above and viewing close doubles in focus at absurdly high barlowed-powers of 371x, 502x, and 819x both eyepieces really showed no weakness. My impression at the higher powers is that the Nagler has a slightly better transmission of light (clarity) while the Radian produced slightly tighter star images (sharpness). However having said that please keep in mind that, 1) I could be wrong, 2) these are so slight (if they exist at all) that it might be associated with just the two individual eyepieces tested and have no relevance in comparing the two types of eyepieces (Naglers vs. Radians) and 3) it just does not matter since under usable magnifications I could not detect any difference. Any real consideration of whether to buy a 5mm Nagler or a 5mm Radian should be done based only on the eye-relief versus the field-of-view.
CONCLUSION: The new 5mm Nagler type 6 eyepiece is a significant improvement over the older 4.8mm Nagler. It has no faults that I can see. If you are looking for a high end, best that money can buy eyepiece, in the 5mm range, and demand that Nagler space walk experience, then I fully expect that this is the eyepiece that you will end up getting.
RECOMMENDATION: For even the most discriminating observer the 5mm Nagler, 5mm Radian, and the 3-6mm Nagler Zoom will provide equal sharpness and clarity. One TeleVue eyepiece does not have any real advantage over the other for planets, double stars, or deep sky when it comes to image quality. Therefore, anyone in the market for a high end, top of the line eyepiece in the 5mm range, is in for a real tough decision. My personal, very unqualified recommendations are:
If you already own a 4.8mm Nagler you may wish to keep it for historical reasons but replace it in your eyepiece case with a 5mm Nagler, or 5mm Radian, or the Nagler 3-6mm Zoom.
If you need or want to wear eyeglasses buy the 5mm Radian. [As with the new 7mm Nagler, this rule is not set in stone. Some may find that when using the new 7mm and 5mm Naglers with glasses (because of the 12mm of eye-relief) that the reduced F.o.V. with glasses is close to that of a Radian's total F.o.V. with or without glasses. If this is the case then I would recommend the new 5mm Nagler over the 5mm Radian since you will always have the option of still wearing your glasses with a F.o.V. equal to that of a Radian or removing your glasses and enjoying the full 82 degree field-of-view that only a Nagler can provide.]
If you do not wish to wear eyeglasses and you just can't live without the wide-field-of-view then get the 5mm Nagler type 6 eyepiece. Those that specialize in observing extended deep sky objects at high power using a telescope on an alt azimuth mount may prefer this eyepiece.
If you do not wish to wear eyeglasses and think that the advantages of a zoom might be as important as a wide-field-of-view then consider the Nagler-Zoom. Those that specialize in the planets and use clock driven telescopes may prefer the Zoom because of its ability to micro-tune magnification at extreme high powers against atmospheric conditions.
Richard Orr 7 September, 2001